Exhibit
4.1


THIRD
SUPPLEMENTAL INDENTURE


THIS
THIRD SUPPLEMENTAL INDENTURE (this “Third Supplemental
Indenture”) is entered into as of June 4 2007 among ERP OPERATING
LIMITED PARTNERSHIP, an Illinois limited partnership (the “Partnership”),
having its principal offices at Two North Riverside Plaza, Suite 400,
Chicago, Illinois 60606, and THE BANK OF NEW YORK TRUST COMPANY, N.A. (as
successor in trust to J.P. Morgan Trust Company, National Association, as
successor in trust to Bank One Trust Company, NA, as successor to The First
National Bank of Chicago), a bank duly organized and existing under the laws of
the United States, as Trustee hereunder (the “Trustee”),
having a Corporate Trust Office at 2 North LaSalle Street, Suite 1020, Chicago,
Illinois 60602, Attention: Global Corporate Trust


WHEREAS, the Partnership
and the Trustee entered into that certain Indenture, dated as of October 1,
1994 (the “Original Indenture”), the First
Supplemental Indenture thereto, dated as of September 9, 2004 (the “First Supplemental Indenture”) and the Second
Supplemental  Indenture thereto, dated as
of August 23, 2006 (the “Second Supplemental
Indenture”), relating to the Partnership’s senior debt securities
(the “Securities”);


WHEREAS, pursuant to
Section 901 of the Indenture, the Partnership and the Trustee may enter
into supplemental indentures to establish the terms and provisions of a series
of Securities issued pursuant to the Indenture;


WHEREAS, pursuant to
Section 301 of the Indenture, the Partnership desires to establish the
terms of Securities of all series created on or after the date of this Third
Supplemental Indenture; and


WHEREAS, the Partnership
and the Trustee have duly authorized the execution and delivery of this Third
Supplemental Indenture to establish the terms of the Securities created on or
after the date of this Third Supplemental Indenture, have done all things
necessary to make this Third Supplemental Indenture (together with the Original
Indenture, the First Supplemental Indenture and the Second Supplemental
Indenture, the “Indenture”) a valid agreement of
the parties hereto, in accordance with its terms, and the Partnership has
complied with all covenants and conditions precedent to the execution and
delivery of this Third Supplemental Indenture;


NOW,
THEREFORE, in consideration of the premises and the covenants and agreements
contained herein, and for other good and valuable consideration the receipt of
which is hereby acknowledged, and for the equal and proportionate benefit of
the Holders of the Securities, the Partnership and the Trustee agree as
follows:


ARTICLE I


RELATION TO BASE INDENTURE; DEFINITIONS


Section 1.1             Relation to Base Indenture.  This Third
Supplemental Indenture constitutes an integral part of the Indenture.


Section 1.2             Definitions.  For all purposes of
this Third Supplemental Indenture, except as otherwise expressly provided for
or unless the context otherwise requires:













(1)                                  Capitalized
terms used but not defined herein shall have the respective meanings assigned
to them in the Indenture;


(2)                                  The
definition of the term “Total Assets” provided for herein applies solely to
this Third Supplemental Indenture and the covenants set forth in
Article II hereof; and


(3)                                  All
references herein to Articles and Sections, unless otherwise specified, refer
to the corresponding Articles and Sections of this Third Supplemental
Indenture.


“Acquired Debt” means
Debt of a Person (i) existing at the time such Person becomes a Subsidiary
or (ii) assumed in connection with the acquisition of assets from such
Person, in each case, other than Debt incurred in connection with, or in
contemplation of, such Person becoming a Subsidiary or such acquisition.  Acquired Debt shall be deemed to be incurred
on the date of the related acquisition of assets from any Person or the date
the acquired Person becomes a Subsidiary.


“Capitalization Rate”
means 6.75%.


“Capitalized Property
Value” means, as of any date, the aggregate sum of all Property EBITDA for each
such property for the prior four quarters and capitalized at the applicable
Capitalization Rate, provided, however, that if the value of a particular
property calculated pursuant to this clause is less than the undepreciated book
value of such property determined in accordance with GAAP, such undepreciated
book value shall be used in lieu thereof with respect to such property.  “Property EBITDA” is defined as, for any
period of time, without duplication net earnings (loss), excluding net
derivative gains (losses) and gains (losses) on dispositions of real estate,
before deductions for the Partnership and its Subsidiaries (including amounts
reported in discontinued operations) for (i) interest expense (including
prepayment penalties); (ii) provision for taxes based on income;
(iii) depreciation, amortization and all other non-cash items, as
determined in good faith by the Partnership, deducted in arriving at net income
(loss); (iv) extraordinary items; (v) non-recurring items, as
determined in good faith by the Partnership; and (vi) minority interest.  In each case for such period, amounts will be
as reasonably determined by the Partnership in accordance with GAAP, except to
the extent GAAP is not applicable with respect to the determination of non-cash
and non-recurring items.  For purposes of
this definition, Property EBITDA will not include corporate level general and
administrative expenses and other corporate expenses such as land holding
costs, employee and trustee stock and stock option expense and pursuit cost
write-offs as determined in good faith by the Partnership.


“Consolidated EBITDA”
means, for any period of time, without duplication, net earnings (loss),
including the net incremental gains (losses) on sales of condominium units,
vacant land and other non-depreciated real property and excluding net
derivative gains (losses) and gains (losses) on dispositions of REIT
depreciable real estate investments as reflected in the reports filed by the
Partnership under the Exchange Act, before deductions for the Partnership and
its Subsidiaries (including amounts reported in discontinued operations) for
(i) interest expense (including prepayment penalties); (ii) provision
for taxes based on income; (iii) depreciation,



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amortization and all
other non-cash items, as determined in good faith by the Partnership, deducted
in arriving at net income (loss); (iv) extraordinary items;
(v) non-recurring items, as determined in good faith by the Partnership;
and (vi) minority interest.  In each
case for such period, amounts will be as reasonably determined by the
Partnership in accordance with GAAP, except to the extent GAAP is not
applicable with respect to the determination of non-cash and non-recurring
items.  Consolidated EBITDA will be
adjusted, without duplication, to give pro forma effect:  (x) in the case of any assets having been
placed-in-service or removed from service since the beginning of the period and
on or prior to the date of determination, to include or exclude, as the case
may be, any Consolidated EBITDA earned or eliminated as a result of the
placement of such assets in service or removal of such assets from service as
if the placement of such assets in service or removal of such assets from
service occurred at the beginning of the period; and (y) in the case of
any acquisition or disposition of any asset or group of assets since the
beginning of the period and on or prior to the date of determination,
including, without limitation, by merger, or share or asset purchase or sale,
to include or exclude, as the case may be, any Consolidated EBITDA earned or
eliminated as a result of the acquisition or disposition of those assets as if
the acquisition or disposition occurred at the beginning of the period.


“Stabilized Property”
means (i) with respect to an acquisition of an income producing property,
a property becomes stabilized when the Partnership or its Subsidiaries have
owned the property for at least four (4) full quarters and (ii) with
respect to new construction or redevelopment property, a property becomes
stabilized four (4) full quarters after the earlier of (a) eighteen (18)
months after substantial completion of construction or redevelopment, and
(b) the quarter in which the physical occupancy level of the property is
at least ninety-three percent (93%).


“Total Assets” means the
sum of:  (1) for Stabilized Properties,
Capitalized Property Value; and (2) for all other assets of the
Partnership and its Subsidiaries, undepreciated book value as determined in
accordance with GAAP (but excluding accounts receivable and intangibles).


“Total Unencumbered
Assets” means the sum of:  (1) the
Capitalized Property Values of Stabilized Properties not subject to an
encumbrance and (2) for all other assets of the Partnership and its
Subsidiaries not subject to an encumbrance, undepreciated book value of such
assets as determined in accordance with GAAP (but excluding accounts receivable
and intangibles).


“Unsecured Debt” means
all Debt of the Partnership and its Subsidiaries except Secured Debt.



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ARTICLE II


LIMITATIONS ON INCURRENCE OF DEBT


In lieu of the covenants set forth in Section
1004 of the Original Indenture and Article Two of the First Supplemental
Indenture, which shall not apply to the Future Securities (as defined below),
there are established the following covenants for the benefit of the Holders of
each series of Securities issued subsequent to the date hereof (“Future Securities”) and to which such
Future Securities shall be subject:


Section 2.1             The Partnership will not, and will
not permit any Subsidiary to, incur any Debt, other than intercompany Debt
(representing Debt to which the only parties are the Company, the Partnership
and/or any of its Subsidiaries (but only so long as such Debt is held solely by
any of the Company, the Partnership and any Subsidiary)) that is subordinate in
right of payment to the Securities, if, immediately after giving effect to the
incurrence of such additional Debt and the application of the proceeds thereof,
Debt would exceed 65% of Total Assets at the reporting date.


Section 2.2             In addition to the limitations set
forth in Section 2.1 of this Third Supplemental Indenture, the Partnership
will not, and will not permit any Subsidiary to, incur any Debt if the ratio of
Consolidated EBITDA to the Maximum Annual Service Charge for the four
consecutive fiscal quarters most recently ended prior the date on which such
additional Debt is to be incurred shall have been less than 1.5, on a pro forma
basis after giving effect thereto and to the application of the proceeds
therefrom, and calculated on the assumption that (i) such Debt and any
other Debt incurred by the Partnership and its Subsidiaries since the first day
of such four-quarter period and the application of the proceeds therefrom,
including to refinance other Debt, had occurred at the beginning of such
period; (ii) the repayment or retirement of any other Debt by the
Partnership and its Subsidiaries since the first day of such four-quarter
period had been repaid or retired at the beginning of such period (except that,
in making such computation, the amount of Debt under any revolving credit
facility shall be computed based upon the average daily balance of such Debt
during such period); (iii) in the case of Acquired Debt or  Debt incurred in connection with any acquisition since the
first day of such four-quarter period, the related acquisition had occurred as
of the first day of such period with the appropriate adjustments with respect
to such acquisition being included in such pro forma calculation; (iv) any
income earned as a result of any increase in Total Assets since the end of such
four-quarter period had been earned, on an annualized basis, for such period;
and (v) in the case of any acquisition or disposition by the Partnership
or its Subsidiaries of any asset or group of assets since the first day of such
four-quarter period, whether by merger, stock purchase or sale, or asset
purchase or sale, such acquisition or disposition or any related repayment of
Debt had occurred as of the first day of such period with the appropriate
adjustments with respect to such acquisition or disposition being included in
such pro forma calculation.


Section 2.3             In addition to the limitations set
forth in Sections 2.1 and 2.2 of this Third Supplemental Indenture, the
Partnership will not, and will not permit any Subsidiary to, incur any Debt
secured by any mortgage, lien, charge, pledge, encumbrance or security interest
of any kind upon any of the property of the Partnership or any Subsidiary,
whether owned at the date hereof or hereafter acquired, if, immediately after
giving effect to the incurrence of such 



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additional Debt and the
application of the proceeds thereof, the aggregate principal amount of all
outstanding Debt of the Partnership and its Subsidiaries on a consolidated
basis which is secured by any mortgage, lien, charge, pledge, encumbrance or
security interest on property of the Partnership or any Subsidiary is greater
than 40% of the Partnership’s Total Assets.


Section 2.4             In addition to the limitations set
forth in Sections 2.1, 2.2 and 2.3 of this Third Supplemental Indenture,
the Partnership shall maintain Total Unencumbered Assets of not less than 125%
of the aggregate outstanding principal amount of the Partnership’s Unsecured
Debt.


Section 2.5             For purposes of this Article Two,
Debt shall be deemed to be “incurred” by the Partnership or a Subsidiary
whenever the Partnership or such Subsidiary shall create, assume, guarantee or
otherwise become liable in respect thereof.


ARTICLE III


MISCELLANEOUS PROVISIONS


Section 3.1             Counterparts.  This Third Supplemental Indenture may be
executed in counterparts, each of which shall be deemed an original, but all of
which shall together constitute one agreement binding on all parties hereto,
notwithstanding that all the parties have not signed the same counterpart.


Section 3.2             Trustee’s Acceptance.  The Trustee hereby accepts this Third
Supplemental Indenture and agrees to perform the same under the terms and
conditions set forth in the Indenture.


Section 3.3             Reference to the Effect on the
Indenture.


(a)           On
and after the effective date of this Third Supplemental Indenture, each
reference in the Indenture to “this Indenture,” “hereunder,” “hereof,” or “herein”
shall mean and be a reference to the Indenture as supplemented by this Third
Supplemental Indenture unless the context otherwise requires.


(b)           Except
as specifically modified or amended by this Third Supplemental Indenture, the
Indenture is in all respects ratified and confirmed and all the terms,
conditions and provisions thereof shall remain in full force and effect.  Upon the execution and delivery of this Third
Supplemental Indenture by the Partnership and the Trustee, this Third
Supplemental Indenture shall form a part of the Indenture for all
purposes.  Any and all references,
whether within the Indenture or in any notice, certificate or other instrument
or document, shall be deemed to include a reference to this Third Supplemental
Indenture (whether or not made), unless the context shall otherwise require.


Section 3.4             Governing Law.  THIS THIRD SUPPLEMENTAL INDENTURE SHALL BE
GOVERNED BY, AND CONSTRUED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF NEW
YORK (WITHOUT GIVING EFFECT TO THE CONFLICT OF LAWS PRINCIPLES THEREOF).



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Section 3.5             Trust Indenture Act Controls.  If any provision of this Third Supplemental
Indenture limits, qualifies or conflicts with another provision of this Third
Supplemental Indenture or the Indenture that is required to be included by the
Trust Indenture Act of 1939, as amended (the “Act”),
as in force at the date this Third Supplemental Indenture is executed, the
provision required by the Act shall control.


Section 3.6             Benefits of Third Supplemental
Indenture or the Securities.  Nothing
in this Third Supplemental Indenture or the Securities, express or implied,
shall give to any Person, other than the parties hereto and thereto and their
successors hereunder and thereunder and the Holders of the Securities, any
benefit of any legal or equitable right, remedy or claim under the Indenture,
this Third Supplemental Indenture or the Securities.


Section 3.7             Successors.  All agreements of the Partnership in this
Third Supplemental Indenture shall bind its successors.  All agreements of the Trustee in this Third
Supplemental Indenture shall bind its successors.


Section 3.8             Concerning the Trustee.  The Trustee shall not be responsible for any
recital herein (other than the fourth recital as it applies to the Trustee) as
such recitals shall be taken as statements of the Partnership, or the validity
of the execution by the Partnership of this Third Supplemental Indenture.  The Trustee makes no representations as to
the validity or sufficiency of this Third Supplemental Indenture.


Section 3.9             Certain Duties and
Responsibilities of the Trustee.  In
entering into this Third Supplemental Indenture, the Trustee shall be entitled
to the benefit of every provision of the Indenture relating to the conduct or
affecting the liability or affording protection to the Trustee, whether or not
elsewhere herein so provided.


Section 3.10           Titles.  Section titles are for descriptive purposes
only and shall not control or alter the meaning of this Third Supplemental
Indenture as set forth in the text.


Section 3.11           Severability.  In case any one or more of the provisions in
this Third Supplemental Indenture shall be held invalid, illegal or
unenforceable, in any respect for any reason, the validity, legality and
enforceability of any such provision in every other respect and of the
remaining provisions shall not in any way be affected or impaired thereby, it
being intended that all of the provisions hereof shall be enforceable to the
full extent permitted by law.


[signature
page follows]



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IN WITNESS WHEREOF, the
parties hereto have caused this Third Supplemental Indenture to be duly
executed as of the day and year first above written.


	
  

  	
  ERP OPERATING LIMITED PARTNERSHIP

  
	
   

  	
   

  	
   

  
	
   

  	
  By:

  	
  Equity Residential, its General Partner

  
	
   

  	
   

  	
   

  
	
   

  	
   

  	
   

  
	
   

  	
  By:

  	
   

  
	
   

  	
   

  	
  Name:

  
	
   

  	
   

  	
  Title:

  
	
   

  	
   

  
	
   

  	
   

  
	
   

  	
  THE BANK OF NEW YORK TRUST COMPANY, N.A., as Trustee

  
	
   

  	
   

  	
   

  
	
   

  	
   

  	
   

  
	
   

  	
  By:

  	
   

  
	
   

  	
   

  	
  Name:

  
	
   

  	
   

  	
  Title:

  



 



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