Most governments keep balance of payments statistics on exports and imports by value, and construct international price indexes in order to deflate these statistics. How can intrafirm trades, trade between related parties, bias the construction of these international price indexes? Does transfer pricing, the price of products traded between related party firms, bias the export and import price indexes in any predictable fashion? If firms manipulate transfer prices to avoid taxes or tariffs, what is the appropriate transfer price to use in constructing export and import price indexes, in theory and in practice? These issues are important because related party trade is large, representing half of U.S. imports and one-third of U.S. exports, and perhaps a third of worldwide merchandise trade flows. This paper explains how transfer pricing and intrafirm trade can bias the construction of export and import price indexes, outlines and evaluates the various prices that could be used to construct these indexes, and makes some recommendations for the international price program run by the U.S. Bureau of Labor Statistics.