This book not only covers fixed point theory, variational inequalities, and vector optimization, but also explains the connections between them, enabling the study of a general form of variational inequality problems related to the optimality conditions involving differentiable or directionally differentiable functions. Packed with detailed proofs, the text supplies an introduction to the field and a guideline to the literature, progressing from basic concepts to the latest developments. It provides fundamental knowledge of directional derivatives and monotonicity required in understanding and solving variational inequality problems.