Semiotics, in its many forms, presents a rich and multifaceted framework for comprehending many different kinds of natural and artificial processes. A naturalistic framework is presented for explaining how signs realize basic informational functions in biological organisms, social organizations, and artificial devices. A theory of functional semiotics attempts to answer basic questions about organization and semiotic function, such as what properties must material systems have in order to support signs and sign functions? How can semiotic processes in natural, social, and artificial worlds be distinguished from nonsemiotic processes? Such a theory also seeks to address more complex theoretical issues: What kinds of semiotic functions are possible? What are the organizational requisites for meaning and purpose? Are there neurosemiotic requisites conscious awareness?This chapter outlines a broad theory of sign use in natural and artificial systems that was developed over several decades within the context of theoretical biology, cybernetics, systems theory, biosemiotics, and neuroscience (Cariani 1989(Cariani , 2001a(Cariani , b, 2011.It begins with a survey of different approaches to semiosis in nature. General functional properties of and operations on signs are then discussed, beginning with the use of signs in computers and formal systems followed by a semiotic description of the operational structure of scientific models that illustrates sign-mediated syntax, semantic, and pragmatic relations in observers.The framework is then expanded to cover percept-action loops in animals and robots by including sign-directed action on the external world. Simple percept-action loops can be elaborated by incorporating sign mechanisms that permit flexible mappings between percepts and actions. These coordinative mechanisms include memory mechanisms, which allow actions to be contingent on past percepts, and