The chapter provides an overview of fluctuating asymmetry (FA) and developmental stability, emphasizing the importance of understanding subtle departures from symmetry in bilateral organisms. FA is a measure of developmental stability, reflecting how well an organism can produce an 'ideal' form under specific conditions. The chapter discusses the three common patterns of right-left (R-L) frequency distributions: FA, directional asymmetry (DA), and antisymmetry. FA is characterized by small, random variations in symmetry, while DA and antisymmetry involve more systematic deviations. The chapter highlights the critical assumption that FA should not have a heritable basis to ensure that differences in asymmetry among individuals are solely due to environmental or genetic factors. It also addresses the challenges in comparing FA data across studies due to measurement errors and sample sizes, and provides recommendations for conducting FA analyses with precision and avoiding common pitfalls. The terminology section clarifies the distinction between individual asymmetry and the pattern of asymmetry variation in a sample, suggesting the use of terms like "subtle asymmetry" to describe slight departures from symmetry in an individual without making assumptions about the distribution.The chapter provides an overview of fluctuating asymmetry (FA) and developmental stability, emphasizing the importance of understanding subtle departures from symmetry in bilateral organisms. FA is a measure of developmental stability, reflecting how well an organism can produce an 'ideal' form under specific conditions. The chapter discusses the three common patterns of right-left (R-L) frequency distributions: FA, directional asymmetry (DA), and antisymmetry. FA is characterized by small, random variations in symmetry, while DA and antisymmetry involve more systematic deviations. The chapter highlights the critical assumption that FA should not have a heritable basis to ensure that differences in asymmetry among individuals are solely due to environmental or genetic factors. It also addresses the challenges in comparing FA data across studies due to measurement errors and sample sizes, and provides recommendations for conducting FA analyses with precision and avoiding common pitfalls. The terminology section clarifies the distinction between individual asymmetry and the pattern of asymmetry variation in a sample, suggesting the use of terms like "subtle asymmetry" to describe slight departures from symmetry in an individual without making assumptions about the distribution.