Abstract
In this chapter we recall some essential definitions and results concerning the group GSp(4)\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$\mathrm {GSp}(4)$$\end{document} over a nonarchimedean local field of characteristic zero and its representation theory. We also review the theory of paramodular vectors.