In this technical lecture, we will discuss the fundamentals of noise processes within an oscillator and the associated design insights. We will start with understanding evolution of noise from device and external noise sources to phase noise. We will develop the time-varying phase noise model, discuss some of the nuances involved in it, and how a deeper understanding of that process can help us identify additional intuition in design of voltage controlled oscillators (VCO). We will investigate specific applications of this model to various kinds of oscillators, such as LC ad ring VCOs and how it fits with the general picture of frequency generation.