4th Annual Lobanov-Rostovsky Lecture in Planetary Geology delivered by Professor John Grotzinger, Caltech, USA The Mars Science Laboratory rover, Curiosity, touched down on the surface of Mars on August 5, 2012. Curiosity was built to search and explore for habitable environments and has a lifetime of at least one Mars year (~23 months), and drive capability of at least 20 km. The MSL science payload can assess ancient habitability which requires the detection of former water, as well as a source of energy to fuel microbial metabolism, and key elements such carbon, sulfur, nitrogen, and phosphorous. The search for complex organic molecules is an additional goal and our general approach applies some of the practices that have functioned well in exploration for hydrocarbons on Earth. The selection of the Gale Crater exploration region was based on the recognition that it contained multiple and diverse objectives, ranked with different priorities, and thus increasing the chances of success that one of these might provide the correct combination of environmental factors to define a potentially habitable paleoenvironment. Another important factor in exploration risk reduction included mapping the landing ellipse ahead of landing so that no matter where the rover touched down, our first drive would take us in the direction of a science target deemed to have the greatest value as weighed against longer term objectives, and the risk of mobility failure. Within 8 months of landing we were able to confirm full mission success. This was based on the discovery of fine-grained sedimentary rocks, inferred to represent an ancient lake. These Fe-Mg-rich smectitic mudstones preserve evidence of an aqueous paleoenvironment that would have been suited to support a Martian biosphere founded on chemolithoautotrophy and characterized by neutral pH, low salinity, and variable redox states of both iron and sulfur species. The environment likely had a minimum duration of hundreds to tens of thousands of years. In the past year simple chlorobenzene and chloroalkane molecules were confirmed to exist within the mudstone. These results highlight the biological viability of fluvial-lacustrine environments in the ancient history of Mars and the value of robots in geologic exploration.