We like to think of enterprise architecture (EA) as system engineering for the enterprise. Sources differ on the definition of EA:

ISO/IEC 42010: 2007  defines ‘‘architecture’’ as: ‘‘the fundamental organization of a system, embodied in its components, their relationships to each other and the environment, and the principles governing its design and evolution.’’

TOGAF® defines the term Architecture as having two meanings depending upon the context:

• A formal description of a system or a detailed plan of the system at component level to guide its implementation.
• The structure of components, their inter-relationships and the principles and guidelines governing their design and evolution over time.

Wikipedia  sum EA up in the following way:

“To some, 'enterprise architecture' refers either to the structure of a business, or the documents and diagrams that describe that structure. To others, 'enterprise architecture' refers to the business methods that seek to understand and document that structure. A third use of 'enterprise architecture' is a reference to a business team that uses EA methods to produce architectural descriptions of the structure of an enterprise.“

Our experienced EA practitioners are TOGAF 9 certified and generally use the framework when assisting customers with EA.

Below is an extract from TOGAF 9.1 Introduction Chapter addressing the need for EA:

Why do I need an enterprise architecture?

The purpose of enterprise architecture is to optimize across the enterprise the often fragmented legacy of processes (both manual and automated) into an integrated environment that is responsive to change and supportive of the delivery of the business strategy.

Today's CEOs know that the effective management and exploitation of information through IT is a key factor to business success, and an indispensable means to achieving competitive advantage. An enterprise architecture addresses this need, by providing a strategic context for the evolution of the IT system in response to the constantly changing needs of the business environment.

Furthermore, a good enterprise architecture enables you to achieve the right balance between IT efficiency and business innovation. It allows individual business units to innovate safely in their pursuit of competitive advantage. At the same time, it ensures the needs of the organization for an integrated IT strategy are met, permitting the closest possible synergy across the extended enterprise.

The advantages that result from a good enterprise architecture bring important business benefits, which are clearly visible in the net profit or loss of a company or organization:

• A more efficient business operation:
  • Lower business operation costs
  • More agile organization
  • Business capabilities shared across the organization
  • Lower change management costs
  • More flexible workforce
  • Improved business productivity
• A more efficient IT operation:
  • Lower software development, support, and maintenance costs
  • Increased portability of applications
  • Improved interoperability and easier system and network management
  • Improved ability to address critical enterprise-wide issues like security
  • Easier upgrade and exchange of system components
• Better return on existing investment, reduced risk for future investment:
  • Reduced complexity in the business and IT
  • Maximum return on investment in existing business and IT infrastructure
  • The flexibility to make, buy, or out-source business and IT solutions
  • Reduced risk overall in new investments and their cost of ownership
• Faster, simpler, and cheaper procurement:
• Buying decisions are simpler, because the information governing procurement is readily available in a coherent plan
• The procurement process is faster - maximizing procurement speed and flexibility without sacrificing architectural coherence
• The ability to procure heterogeneous, multi-vendor open systems
• The ability to secure more economic capabilities