The state constitution establishes the structure and purpose of the Texas government. The current constitution took effect on February 15, 1876.
The state legislature can propose amendments to the constitution. Texas voters later decide whether to adopt the proposed amendments. Since 1876, the legislature has proposed hundreds of amendments, the majority of which have been adopted by voters. The Legislative Reference Library has a constitutional amendment search and the Texas Legislative Council offers a table of constitutional amendments since 1876 [PDF].
The current constitution is the seventh 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 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.