The Common Information Model (CIM) is an open standard that defines how managed elements in an IT environment are represented as a common set of objects and relationships between them. This is intended to allow consistent management of these managed elements, independent of their manufacturer or provider.
One way to describe CIM is to say that it allows multiple parties to exchange management information about these managed elements. However, this falls short in expressing that CIM not only represents these managed elements and the management information, but also provides means to actively control and manage these elements. By using a common model of information, management software can be written once and work with many implementations of the common model without complex and costly conversion operations or loss of information.
The CIM standard includes the CIM Infrastructure Specification and the CIM Schema:
CIM Infrastructure Specification
The CIM Infrastructure Specification defines the architecture and concepts of CIM, including a language by which the CIM Schema (including any extension schema) is defined, and a method for mapping CIM to other information models, such as SNMP. The CIM architecture is based upon UML, so it is object-oriented: The managed elements are represented as CIM classes and any relationships between them are represented as CIM associations. Inheritance allows specialization of common base elements into more specific derived elements.
The CIM Schema is a conceptual schema which defines the specific set of objects and relationships between them that represent a common base for the managed elements in an IT environment. The CIM Schema covers most of today's elements in an IT environment, for example computer systems, operating systems, networks, middleware, services and storage. The CIM Schema defines a common basis for representing these managed elements. Since most managed elements have product and vendor specific behavior, the CIM Schema is extensible in order to allow the producers of these elements to represent their specific features seamlessly together with the common base functionality defined in the CIM Schema.
CIM is the basis for most of the other DMTF standards (e.g. WBEM or SMASH). It is also the basis for the SMI-S standard for storage management.
Updates to the CIM Schema are published regularly. 
Version 2.35.0 of the CIM Schema was published on January 7, 2013.
Version 2.34.0 of the CIM Schema was published on September 6, 2012.
Version 2.33.0 of the CIM Schema was published on June 28, 2012.
Version 2.32.0 of the CIM Schema was published on April 17, 2012.
Version 2.31.1 of the CIM Schema was published on April 4, 2012.
Version 2.31.0 of the CIM Schema was published on December 22, 2011.
Version 2.30.0 of the CIM Schema was published on September 27, 2011.
Version 2.29.0 of the CIM Schema was published on June 3, 2011.
Version 2.28.0 of the CIM Schema was published on February 2, 2011.
Version 2.27.0 of the CIM Schema was published on November 15, 2010.
Version 2.26.0 of the CIM Schema was published on July 21, 2010.
Version 2.25.0 of the CIM Schema was published on March 31, 2010.
Version 2.6 of the CIM Infrastructure Specification was published on March 31, 2010.
Version 1.1 of the CIM Compliance Specification was published on December 15, 2003.
Version 2.2 of the CIM Specification was published on June 14, 1999.
Many vendors provide implementations of CIM in various forms:
Some operating systems provide a CIM implementation, for example:
CIM-XML is a protocol for performing sending CIM messages on top of HTTP. It has two message types: Operational messages, which provoke a response from the receiver (RPC), and Export Messages, which are indications/events. It is a part of the WBEM protocol family, and is standardised by the DMTF.