Serd is a lightweight C library for RDF syntax which supports reading and writing Turtle and NTriples. Serd (and the included serdi tool) can be used to stream abbreviated Turtle. Serd can serialise an unbounded amount of abbreviated Turtle using a fixed amount of memory, and it does so very quickly. Serd is written to the Turtle, NTriples and URI specifications, and includes a comprehensive test suite which includes all the tests from the Turtle specification.