The Mars Science Laboratory rover Curiosity launched from Cape Canaveral, Florida on November 26, 2011 and landed in Gale crater on August 6, 2012. Gale crater is ~150 km wide and is located near the equator, along the boundary between the ancient "Southern Highlands" of Mars and the younger "Northern Lowlands." At the center of the crater is a ~5 km high mountain of layered sedimentary rocks known as Mount Sharp, and these rocks contain minerals that are key to understanding ancient environments and climate change on Mars. The lowest layers of rock contain clay minerals, which, on Earth, generally form in environments with abundant liquid water. The rocks above the clay-bearing units contain sulfate minerals, which require less water to form and precipitate from saline, and potentially acidic, solutions. This stratigraphy of minerals, with sulfate-bearing rocks on top of (and thus younger than) clay-bearing rocks, is common across Mars, and marks a major climatic change more than 3 billion years ago. Curiosity is gradually driving up the flanks of Mount Sharp and studying the rocks and sediments with cameras and instruments that can help scientists identify minerals, determine chemical compositions, and search for the presence of organic molecules. With this information, scientists will interpret the ancient environments of Mars and search for evidence that these environments may have been habitable.