Research resources on constitutions and constitutional change:

The Constitution Net
The Constitution Net is a project created to support legislators, constitutional lawyers and other constitutional practitioners in finding useful and relevant information, sharing knowledge and building a community of best practice.
http://constitutionnet.org

CONSTITUTE
Constitute was developed by the authors of the Comparative Constitutions Project at the University of Texas at Austin. It has has the most comprehensive database of the worlds constitutions, past and present.
https://www.constituteproject.org

The Comparative Constitutions Project
The Comparative Constitutions Project launched Constitute in collaboration with Google Ideas in 2013. Comparative Constitutions Project’s website is.
https://comparativeconstitutionsproject.org