Abstract: Methods, systems, and computer storage media for providing observation stream data of security incidents using an observation stream engine in a security management system. An observation stream framework supports continuously generating and presenting observation stream data that facilitates developing a working hypothesis of an active security incident. The observation stream framework can also include observation stream query-types that can be selected for running queries against a plurality of security data sources. In operation, an observation stream query is accessed. The observation stream query is a user-generated observation stream query associated with an observation stream query-type. The observation stream query-type comprises parameters for querying a plurality of security data sources and dynamic tracking of a security incident. The observation stream query is executed and observation stream data is generated.