This book offers a unified perspective on the latest developments in the theory of one-dimensional singular integral equations and systems of such equations. It complements the classic monograph by N. I. Mushelishvili, *Singular Integral Equations* (Moscow: Nauka, 1968), which focuses on equations of the normal type. In this work, special attention is given to equations with symbols that tend to zero—those that do not fall into the normal category. The author employs methods from functional analysis, with necessary background provided in the introduction. Ideal for specialists in classical and functional analysis, this book is also accessible to advanced students majoring in mathematics.