A modular stent graft system including: a first stent graft including a first tubular body of biocompatible graft material, a proximal end, a distal end and a first interface region having an internal surface and an external surface at the distal end; a first self-expanding locking stent secured to the internal surface of the first interface region, the first locking stent including a series of proximal apices and a series of distal apices, a proximal end having a first diameter and a distal end having a second diameter greater than the first diameter, wherein the first locking stent is secured to the internal surface of the first interface region only at the distal stent apices; a first external stent secured to the graft material of the first stent graft proximally adjacent to the first locking stent; and a second external stent secured to the graft material of the first stent graft distally adjacent to the first locking stent and at the distal most end of the first stent graft; a second stent graft including a second tubular body of biocompatible graft material, a proximal end, a distal end and a second interface region having an internal surface and an external surface at the proximal end configured to at least partially overlap with the first interface region; a second self-expanding locking stent secured to the external surface of the second interface region, the second locking stent including a series of proximal apices, a series of distal apices, a proximal end having a first diameter and a distal end having a second diameter greater than the first diameter, wherein the second locking stent is secured to the external surface of the second interface region only at the proximal stent apices; a proximal stent secured to the graft material of the second stent graft proximally adjacent to the second locking stent; and a distal stent secured to the graft material of the second stent graft distally adjacent to the second locking stent; wherein the first locking stent is configured to receive the second locking stent in an interlocking relationship; and wherein at least a portion of the second locking stent is nested between the first locking stent and the internal surface of the interface region of the first stent graft, the first external stent and the proximal stent longitudinally overlap, and the second external stent and the distal stent longitudinally overlap, when the first and second locking stents are interlocked. a first stent graft including a first tubular body of biocompatible graft material, a proximal end, a distal end and a first interface region having an internal surface and an external surface at the distal end; a first self-expanding locking stent secured to the internal surface of the first interface region, the first locking stent including a series of proximal apices and a series of distal apices, a proximal end having a first diameter and a distal end having a second diameter greater than the first diameter, wherein the first locking stent is secured to the internal surface of the first interface region only at the distal stent apices; a first external stent secured to the graft material of the first stent graft proximally adjacent to the first locking stent; and a second external stent secured to the graft material of the first stent graft distally adjacent to the first locking stent and at the distal most end of the first stent graft; a second stent graft including a second tubular body of biocompatible graft material, a proximal end, a distal end and a second interface region having an internal surface and an external surface at the proximal end configured to at least partially overlap with the first interface region; a second self-expanding locking stent secured to the external surface of the second interface region, the second locking stent including a series of proximal apices, a series of distal apices, a proximal end having a first diameter and a distal end having a second diameter greater than the first diameter, wherein the second locking stent is secured to the external surface of the second interface region only at the proximal stent apices; a proximal stent secured to the graft material of the second stent graft proximally adjacent to the second locking stent; and a distal stent secured to the graft material of the second stent graft distally adjacent to the second locking stent; wherein the first locking stent is configured to receive the second locking stent in an interlocking relationship; and wherein at least a portion of the second locking stent is nested between the first locking stent and the internal surface of the interface region of the first stent graft, the first external stent and the proximal stent longitudinally overlap, and the second external stent and the distal stent longitudinally overlap, when the first and second locking stents are interlocked.