Client Side Object Model (CSOM) was first introduced in SharePoint 2010. The Client Side Object Model is mainly used to build client applications and enable us to access SharePoint Sites that are hosted outside without using webservices. Prior to the CSOM, developers had only a few choices to build client applications. However, this has changed now. With the introduction of CSOM, developers now have more choices and will be able to access the core SharePoint functionalites to a wide extent. In SharePoint 2010, the CSOM exposed the core SharePoint functionalites only whereas in SharePoint 2013, the Microsoft SharePoint team has added a few more assemblies. Now we are able to access the Service Applications using the Client Side Object Model.