We investigate concurrency as unifying computational paradigm which integrates functional, constraint, and object-oriented programming. We propose the Rho-calculus as a uniform foundation of concurrent computation and formally relate it to other models: The Rho-calculus with equational constraints provides for logic variables and is bisimilar to the Gamma-calculus. The Rho-calculus without constraints is a proper subset of the Pi-calculus. We prove its Turing completeness by embedding the eager Lambda-calculus in continuation passing style. The Rho-calculus over an arbitrary constraint system is an extension of the standard cc-model with procedural abstraction.