Carbon capture and sequestration (CCS) is a key technology pathway to substantial reduction of greenhouse gas emissions for the state of California and the western region. Current estimates suggest that the sequestration resource of the state is large, and could safely and effectively accept all of the emissions from large CO2 point sources for many decades and store them indefinitely. This process requires suitable sites to sequester large volumes of CO2 for long periods of time. Site characterization is the first step in this process, and the state will ultimately face regulatory, legal, and technical questions as commercial CCS projects develop and commence operations. The most important aspects of site characterizations are injectivity, capacity, and effectiveness. A site can accept at a high rate a large volume of CO2 and store it for a long time is likely to serve as a good site for geological carbon sequestration. At present, there are many conventional technologies and approaches that can be used to estimate, quantify, calculate, and assess the viability of a sequestration site. Any regulatory framework would need to rely on conventional, easily executed, repeatable methods to inform the site selection and permitting process. The most important targets for long-term storage are deep saline formations and depleted oil and gas fields.