This book introduces non-uniform-sample-based signal processing methods, specifically those derived based on zero-crossing measurements. Most current-day digital signal processing is based on uniform Nyquist sampling of bandlimited signals. However, most real-world signals are neither time-invariant nor bandlimited. In the past few decades, there have been significant developments in different sampling approaches: random sampling, signal-dependent sampling, and compressive sampling, which are promising both for time-varying signals as well as more compact processing in terms of the number of samples and power consumed.