We determine whether a bilateral free trade agreement (FTA) acts as a building block for multilateral free trade (MFT) in a three-country model with asymmetric domestic markets. Our main conclusions are as follows: (i) A bilateral FTA between two large countries can act as a building block for MFT; (ii) A bilateral FTA between two small countries acts as a stumbling block for MFT; (iii) This FTA can be Pareto improving when a multilateral trade agreement is not feasible.