Abstract. This document presents two different paradigms of description of communication behaviour, one focussing on global message flows and another on end-point behaviours, as formal calculi based on session types. The global calculus originates from Choreography Description Language, a web service description language developed by W3C WS-CDL working group. The end-point calculus is a typed π-calculus. The global calculus describes an interaction scenario from a vantage viewpoint; the endpoint calculus precisely identifies a local behaviour of each participant. After introducing the static and dynamic semantics of these two calculi, we explore a theory of endpoint projection which defines three principles for well-structured global description. The theory then defines a translation under the three principles which is sound and complete in the sense that all and only behaviours specified in the global description are realised as communications among end-point processes. Throughout the theory, underlying type structures play a fundamental role. The document is divided in two parts: part I introduces the two descriptive frameworks using simple but non-trivial examples; the second part establishes a theory of the global and end-point formalisms.