The Texas Constitution establishes the structure and purpose of the Texas government. The current Texas Constitution took effect on February 15, 1876. The Constitution is available on the Texas Constitution and Statutes Web site.
During the legislative session, the Texas Legislature can propose constitutional amendments to be voted on by Texas voters. Since 1876, the Legislature has proposed hundreds of amendments, the majority of which have been adopted by voters. The Web site for the Legislative Reference Library (LRL) has a constitutional amendment search and the Texas Legislative Council offers a table of constitutional amendments since 1876 [PDF], arranged numerically by article and section.
The current Texas Constitution is the seventh constitution in Texas history. The previous six were the 1827 Constitution of the State of Coahuila and Tejas, the 1836 Constitution of the Republic of Texas, and different versions of the Constitution of Texas for the years: 1845, 1861, 1866, and 1869. Digital images of these Constitutions as well as additional information are available through "Texas Constitutions 1824-1876," a project of the Tarlton Law Library and the University of Texas at Austin's School of Law.
The Texas State Law Library also has an electronic version of The Constitution of the State of Texas: An Annotated and Comparative Analysis available.