Style guides are internal company documents that aid the design process across multiple products and portfolios. They can help to ensure

• Effective reuse of design and understanding across the portfolio
• Consistency of operation (a major contributor to usability)
• Brand compliance

Style guides can be used at different levels to aid compatibility within

• An entire industry
• A particular company
• Portfolios
• Product platforms

These guides are frequently implemented in a web-based or intranet format and can also be called design pattern libraries.