It evolved from the upper house of the colonial assembly created in 1650 when Maryland was a proprietary colony controlled by Cecilius Calvert. It consisted of the Governor and members of the Governor's appointed council. With slight variation, the body to meet in that form until 1776, when Maryland, now a state independent of British rule, passed a new constitution that created an electoral college to appoint members of the Senate. This electoral college was abolished in 1838 and members began to be directly elected from each county and Baltimore City. In 1972, because of a Supreme Court decision, the number of districts was increased to 47, and the districts were balanced by population rather than being geographically determined.
To serve in the Maryland Senate, a person must be a citizen of Maryland 25 years of age or older. Elections for the 47 Senate seats are held every four years coincident with the federal election in which the President of the United States is not elected. Vacancies are filled through appointment by the Governor. The Senate meets for three months every year; the rest of the year the work of the Senate is light and most members hold another job during this time. It has been controlled by Democrats for a number of years. In the 2006 election, more than two-thirds of the Senate seats were won by Democrats.
Senators elect a President to serve as presiding officer of the legislative body, as well as a President Pro Tempore. The President appoints chairs and membership of six standing committees, four legislative committees as well as the Executive Nominations and Rules Committees. When compared to other state legislatures in the United States, the Maryland Senate has one of the strongest presiding officers and some of the strongest committee chairs. Senators are also organized into caucuses, including party- and demographically-based caucuses. They are assisted in their work by paid staff of the non-partisan Department of Legislative Services and by partisan office staff.