This talk address the problem of noise analysis in RF front-ends of high performance communication systems. The primary distinguishing feature of this approach is that it is based on stochastic analysis where circuit noise sources are modelled as white noise sources with time-varying intensities which act as inputs to the system of differential algebraic equations which describe the circuit. These stochastic differential equations are solved using techniques from stochastic calculus. The solutions of these equations are characterized depending on the underlying circuit structure. As examples, noise analysis results for open loop oscillators, nonlinear circuits in "driven" by noisy oscillators and phase feedback systems such as phase-locked loops will be presented.