General elections are held every even-numbered year (every two years) on the first Tuesday after the first Monday in November. In the general election, depending on the year, voters select national and state executive branch officials and legislators, including president and vice-president, U.S. senators and representatives, state governor and other executive branch officials, and state senators and representatives. Voters also choose a number of other state officeholders in the general election. The website of the Secretary of State lists all of the candidates for upcoming general elections.
General elections in which we choose the president and vice-president (every four years, e.g., 2008, 2012, 2016) always have higher voter turnout than so-called off-year elections. In 1974 Texas adopted a constitutional amendment that extended the term of the Governor and other executive branch offices from two to four years. The amendment also set the election calendar so that these offices would be elected in off-year elections between presidential elections: a practice found in a number of other states as well.
While this change shifted elections for state offices to a cycle that historically has lower voter turnout, it partly insulated the election of state-wide offices from presidential campaigning and national politics. In contrast, all of the seats in the Texas House of Representatives and approximately half of the Texas Senate seats come up for election every two years. So some of these races take place at the same time as the higher-turnout presidential elections.
Special elections are held in Texas for one of three reasons. On the state level, they are called to fill mid-term vacancies in the state Legislature or in a Texas seat in the U.S. Congress. They are also called to vote on proposed amendments to the state Constitution. The great detail of the Texas Constitution means that many proposed policies contradict some element or other in the Constitution, thereby requiring formal constitutional amendments to make minor technical changes as well as the major changes commonly associated with the national amendment process. Over time, the accumulation of amendments simply adds complication and multiplies the probabilities of still more conflicts - and still more amendments.
On the local level, special elections are called to select city council members. Most of the cities in Texas select their council members in this way. As a result of both state tradition and local city charters, these elections are non-partisan - the party affiliation of candidates is not indicated beside their names on the ballot. The absence of partisan "cues" makes it more difficult for voters to choose between candidates.
Amendments to the Constitution are voted on in special elections. It is telling that in the special election of 2003 voters were asked to approve no fewer than 22 amendments to the Constitution. Most of these proposed amendments dealt with trifling issues (like whether to authorize municipalities to donate surplus fire-fighting equipment or supplies for the benefit of rural volunteer fire departments) that would best be decided by executive branch officials or even local governments. In 2007 there were 16 proposed amendments, a significant number of amendments to the state's foundational governmental document.