This review provides an overview of the current empirical knowledge on stellar multiplicity, focusing on Main Sequence (MS) stars and brown dwarfs, as well as populations of Pre-Main Sequence (PMS) stars and embedded protostars. The authors discuss the frequency and characteristics of multiple systems, including orbital periods, mass ratios, and eccentricities, and their dependencies on primary mass and stellar evolutionary stage. They highlight the importance of these studies in probing the star formation process and comparing with numerical and analytical models. The review covers historical surveys, instrumental advancements, and the impact of selection biases and incompleteness on the interpretation of results. It also addresses the multiplicity of different stellar populations, such as solar-type stars, low-mass stars, very low-mass (VLM) stars, intermediate-mass stars, and high-mass stars, detailing their multiplicity frequencies, orbital period distributions, and mass ratio distributions. The section on old and young stars explores the multiplicity properties of Population II stars and open clusters, providing insights into the evolution of stellar multiplicity over time.This review provides an overview of the current empirical knowledge on stellar multiplicity, focusing on Main Sequence (MS) stars and brown dwarfs, as well as populations of Pre-Main Sequence (PMS) stars and embedded protostars. The authors discuss the frequency and characteristics of multiple systems, including orbital periods, mass ratios, and eccentricities, and their dependencies on primary mass and stellar evolutionary stage. They highlight the importance of these studies in probing the star formation process and comparing with numerical and analytical models. The review covers historical surveys, instrumental advancements, and the impact of selection biases and incompleteness on the interpretation of results. It also addresses the multiplicity of different stellar populations, such as solar-type stars, low-mass stars, very low-mass (VLM) stars, intermediate-mass stars, and high-mass stars, detailing their multiplicity frequencies, orbital period distributions, and mass ratio distributions. The section on old and young stars explores the multiplicity properties of Population II stars and open clusters, providing insights into the evolution of stellar multiplicity over time.