Recent advances in cell-free protein expression systems have made them reliable and practical for functional and structural studies of a wide variety of proteins. In particular, wheat germ cell-free translation can consistently produce target proteins in microgram quantities from relatively inexpensive, small-scale reactions. Here we describe our small-scale protein expression method for rapidly producing proteins for functional assay and techniques for determining if the target is suitable for scale-up to amounts potentially needed for structure determination. The cell-free system is versatile and can be easily customized with the inclusion of additives. We describe simple modifications used for producing membrane proteins.