This guideline is focused on building Application / function profiles and specifies a methodology to define Basic Application profiles (BAPs). These Basic Application profiles shall provide a framework for interoperable interaction within or between typical substation automation functions. BAPs are intended to define a subset of mandatory features of IEC 61850 in order to facilitate interoperability in a modular way in practical applications. It is the intention of this guideline to provide a common and generic way to describe the functional behaviour of a specific application function in the domain of substation automation systems as a common denominator of various possible interpretations/implementations of using the standard IEC 61850. The guideline is based on the functional definitions of • IEC 61850-5 “Communication requirements for functions and device models” which gives a comprehensive overview about all application functions needed in a state-of-the-art substation automation implementation. • The Technical Report IEC 61850-7-500 “Basic information and communication structure - Use of logical nodes for modelling applications and related concepts and guidelines for Substations” which illustrates and explains application functions for the substation/protection domain of Logical Nodes in modelling simple and complex functions, to improve common understanding in modelling and data exchange, and finally to lead to interoperable implementations. • The Technical Report IEC 61850-90-3 “Using IEC 61850 for condition monitoring diagnosis and analysis” which gives use cases and data modelling for condition monitoring diagnosis and analysis functions for substation and power grid facilities This guideline does not describe the applications and respective implementation requirements itself, the focus is on their typical information exchange including data and communication services and engineering conventions.