This two-volume collection contains Paulo Ribenboim's work on ordered structures and mathematical logic. Two long unpublished papers and a reproduction of his first book on abelian groups are also featured in these volumes. With over 240 publications, including 13 books, Ribenboim is responsible for some of the most influential research in number theory, mathematical logic, and algebraic structures. Together, these volumes include papers on algebraic structures on directed graphs, real algebraic geometry, applications of model theory in collaboration with Lou van den Dries, and more recent papers with Sibylla Priess-Crampe on mathematical logic programming and Ultrametric spaces. The Ribenboim Prize of the Canadian Number Theory Association is named after him. Paulo Ribenboim is currently professor emeritus at Queen's University in Kingston, Ontario.