Sequences of real or complex numbers are of fundamental importance for mathematics: With their help, the basic concepts of analysis such as continuity and differentiability are explained; these concepts can indeed be formulated for an engineer without the concept of sequences, however, in later chapters we will explain functions using sequences that play a significant role in engineering mathematics, so we cannot completely omit this part of mathematics for engineers. We will, however, keep the presentation brief and only focus on the formulas, rules, properties, and criteria important for understanding.