Directed evolution of antibodies through phage display is a powerful technique for producing binders of various biological targets. One of the recent innovations in the fi eld is the domain antibody, an antibody consisting only of a single variable domain. These anti bodies can be obtained either through immunisation of sharks or camels, or alternatively from recombinant libraries1. The domain antibodies have certain advantages, both pharmacologically and technically. Here we report the construction of a semi-synthetic and highly modular antibody library, based on a human framework (V3-23/D47). The antibody scaffold has been codon optimised to improve expression, and the CDR’s have been created using trinucleotide synthesis. These methods give a strict control over the randomisations, and the ability to design a library with minimal aggregation propensity. To facilitate further manipulation, unique restriction sites have been silently inserted around each CDR. The resulting library has an estimated diversity of 8 x 10^7.