Scope 1: Includes only direct GHG emissions - emissions that result from activities that are owned or controlled by the reporting company. Direct emission can be included under source categories such as Stationary Combustion, Mobile Combustion, Process Emissions, and Fugitive Emissions.
Scope 2: Includes only indirect GHG emissions - emissions that result from organisation activities but occur at sources owned or controlled by another company. Indirect emissions can be reported under source categories including Purchased & Used Electricity, and Purchased Heat & Steam.
Scope 3: Other indirect emissions - emissions that are a consequence of the organisations actions, which occur at sources that you do not own or control and which are not classed as scope 2 emissions. Indirect emissions can be reported under many categories, examples include Business Travel, Employee Commuting, Upstream Transport and Distribution.
More information can be found on the GHG Protocol website.