Medium-chain oleochemicals provide unique capabilities in several market applications. However, the inability of conventional production technologies to achieve onpurpose production of chemicals in this class limits the market supply. Engineering microbial hosts to produce medium-chain free fatty acids provides a novel route to these specialty chemicals. Thus, the aims of my thesis are twofold: 1) To improve the selectivity and activity of various acyl-ACP thioesterases. 2) To engineer superior bacterial hosts which can support the physiological demands imposed by highly active medium-chain acyl-ACP thioesterases. The acyl-acyl carrier protein (acyl-ACP) thioesterase is the key enzyme enabling production of medium-chain oleochemicals in microbial hosts. In the beginning and middle chapters of this work we focus on engineering a ten and twelve carbon-specific acyl-ACP thioesterase to develop free fatty acid production hosts with exclusive selectivity. We used extant datasets to successfully train and use a machine learning model for the identification of acyl-ACP thioesterases with medium-chain substrate specificity from primary sequence information. This ultimately led to the characterization and optimization of the ten-carbon thioesterase from Cuphea lanceolata, ClFatB3 for decanoic acid production in Escherichia coli. We next employed matrix-assisted laser desorption/ionization - mass ii spectrometry (MALDI-MS) technology to develop a high-throughput screening method for the identification of highly selective thioesterases. This facilitated the engineering of the twelve-carbon thioesterase from Umbellularia californica, BTE, for more selective product profiles when expressed in E. coli In the final chapter, we addressed the effects of free fatty acid production on the phospholipid membrane to improve strain robustness and fatty acid yield. We overexpressed a hydroxy-acyl dehydratase from a cyanobacteria to modulate the cell membrane composition. We demonstrated the ability to address the perturbation in the ratio of saturated and unsaturated lipids in fatty acid-producing strains, and we identified a strategy increase the flux of saturated acyl-ACP species through fatty acid biosynthesis.