The Strategic Alignment Model (SAM) of Henderson and Venkatraman [1999] is widely used as the base of Business/IT Alignment theories. The key message of this model, as well as that of many other studies, is that to become a successfull company, one should make sure that the IT strategy is fully aligned with business strategy.
Figure: Strategic Alignment Model [Henderson and Venkatraman, 1999]
The Strategic Alignment Model is composed of four quadrants that consist of three components each. All of the components working together determine the extent of alignment. At least as important are the linkages between the quadrants. The first linkage is that of strategic fit. This is the vertical linkage and refers to the use of strategy to determine the infrastructure of the business. The second linkage is functional integration. This (horizontal) linkage is most directly related to the alignment of business and IT.
Based on this model different perspectives are mentioned, which are shown in the next figure. These perspectives are constructed in a type of triangular format, and can be used to assess the alignment within a company.
Figure: Eight Strategic Alignment Perspectives [Coleman and Papp, 2006]
In addition to these eight perspectives, there are also four fusion perspectives described, that are formed from the combination of two of the individual perspectives. [Luftman, 1996; Coleman and Papp, 2006].
Figure: Fusion Perspectives
Although these different perspectives can be used to gain insights in the way the business and IT are aligned, they provide little guidance on the question how companies can achieve good alignment.
References
Coleman, Preston and Papp, Raymond: Strategic Alignment: Analysis of Perspectives, Proceedings of the 2006 Southern Association for Information Systems Conference, 2006.
Henderson, J.C. and Venkatraman, N.: Strategic Alignment: Leveraging Information Technology for Transforming Organizations, IBM Systems Journal, 1999
Business/IT-Alignment 
[…] Strategic IT alignment In their well-known model, Henderson and Venkatraman (1999) focus on the alignment of IT with business strategy. Simply put, they state that for a […]