Purpose of Review <p>In this article, we review recent literature on the associations between sleep irregularity and a variety of health outcomes and discuss potential mechanisms mediating these relationships.</p> Recent Findings <p>Greater variability in sleep patterns is associated with detriments in sleep quality, circadian rhythms, performance, and both mental and physical health across the lifespan, often beyond contributions from sleep duration alone.</p> Summary <p>A growing consensus in the literature indicates that regularity in sleep timing and duration is important for maintaining optimal health and performance. A variety of published metrics have been proposed to quantify sleep irregularity, and different metrics may be applied based on the types of data available, sample size, length of data collection period, and specific question under investigation. Experimental and longitudinal data establishing a direct causal effect of sleep irregularity on health are limited and remain an important area for future research to develop effective interventions to regularize sleep patterns for better overall health and well-being.</p>