This chapter explores police cooperation through information exchange and analysis. The point of departure is the Norwegian legal basis for information gathering and exchange. Police information-gathering does not need a legal basis unless such gathering means invading a person's privacy, according to the principle of legality, which protects individuals from illegitimate governmental interference. The Schengen Information System II (SIS) is a database available to the police and immigration authorities of Schengen member states. It is designed "to maintain public policy and public security, including national security, in the territories of the Contracting Parties. The SIS was perceived as necessary for common external border control, and to maintain efficient police cooperation in the Schengen Area. SIS II has developed into a more investigative database, including more diverse data – more like traditional national police databases. Some police databases are tools for national police within their territory. Others are international databases, available to national police.