Simply put, Syntax is the study of grammatical relations between words and other units within the sentence (From The Concise Oxford Dictionary of Linguistics, 2 ed.)
Below are some key (online) reference works for syntax.
UBC Library, like most academic libraries, uses Library of Congress Subject Headings. Books on Syntax can be found in the UBC Library catalogue under these Subject Headings:
For books on a specific language, use this format (replace 'French' with whichever language you are interested in):