This document provides an overview of the issues associated with the deployment of service functions (such as firewalls, load balancers, etc.) in large-scale environments. The term service function chaining is used to describe the definition and instantiation of an ordered list of instances of such service functions, and the subsequent "steering" of traffic flows through those service functions. The set of enabled service function chains reflect operator service offerings and is designed in conjunction with application delivery and service and network policy. This document also identifies several key areas that the SFC working group will investigate to guide its architectural and protocol work and associated drafts.