11. Share-Based Compensation
As of March 31, 2019, the Company has four share-based compensation plans and an employee share purchase plan. Prior to the Company’s initial public offering (IPO) in November 2015, the Company granted share-based awards under three share option plans, which were the Mimecast Limited 2007 Key Employee Share Option Plan (the 2007 Plan), the Mimecast Limited 2010 EMI Share Option Scheme (the 2010 Plan), and the Mimecast Limited Approved Share Option Plan (the Approved Plan) (the 2007 Plan, the 2010 Plan and the Approved Plan, collectively, the Historical Plans).
Upon the closing of the IPO, the Mimecast Limited 2015 Share Option and Incentive Plan (the 2015 Plan) and the 2015 Employee Share Purchase Plan (the ESPP) became effective. Subsequent to the IPO, grants of share-based awards have been made under the 2015 Plan and no further grants under the Historical Plans are permitted.
The 2015 Plan allows the compensation committee to make equity-based incentive awards to our officers, employees, non-employee directors and consultants. Initially a total of 5.5 million ordinary shares were reserved for the issuance of awards under the 2015 Plan. This number is subject to adjustment in the event of a share split, share dividend or other change in our capitalization.
The 2015 Plan provides that the number of shares reserved and available for issuance under the plan will automatically increase each January 1st by 5% of the outstanding number of ordinary shares on the immediately preceding December 31 or such lesser number of shares as determined by the board of directors.
Under the 2015 Plan, the share option price may not be less than the fair market value of the ordinary shares on the date of grant and the term of each share option may not exceed 10 years from the date of grant. Share options typically vest over 4 years, but vesting provisions can vary based on the discretion of the board of directors.
The Company settles share option exercises under the 2015 Plan through newly issued shares. The Company’s ordinary shares underlying any awards that are forfeited, canceled, withheld upon exercise of an option, or settlement of an award to cover the exercise price or tax withholding, or otherwise terminated other than by exercise will be added back to the shares available for issuance under the 2015 Plan.
Initially, a total of 1.1 million shares of the Company's ordinary shares were reserved for future issuance under the ESPP. This number is subject to change in the event of a share split, share dividend or other change in capitalization. The ESPP may be terminated or amended by the board of directors at any time.
The ESPP permits eligible employees to purchase shares by authorizing payroll deductions from 1% to 10% of his or her eligible compensation during an offering period, a duration of six months. Unless an employee has previously withdrawn from the offering, his or her accumulated payroll deductions will be used to purchase shares on the last day of the offering period at a price equal to 85% of the fair market value of the shares on the first business day or last business day of the offering period, whichever is lower.
Share-based compensation expense recognized under the 2015 Plan, Historical Plans and ESPP in the accompanying consolidated statements of operations was as follows:
In certain situations, the board of directors has approved modifications to employee share option agreements, including acceleration of vesting or the removal of exercise restrictions for share options for which the service-based vesting has been satisfied, which resulted in additional share-based compensation expense. The total modification expense in the years ended March 31, 2019, 2018 and 2017 was $3.2 million, $0.5 million and $3.0 million, respectively.
Table:
 |  | Year ended March 31, | 
 | 2019 | 2018 | 2017
Cost of revenue  | $1,684 | $1,053 | $1,353
Research and development   | 6,199 | 2,555 | 1,873
Sales and marketing   | 7,856 | 4,477 | 4,719
General and administrative   | 10,215 | 3,649 | 2,349
Total share-based compensation expense | $25,954 | $11,734 | $10,294


Question: What is the change in Research and development expense from Year Ending March 31, 2018 to 2019?
Answer: 3644
Calculation: 6,199-2,555