Heat exchanger networks are widely employed in the chemical processing industries to recover energy, resulting in reduced operating costs. Several methodologies can be found in the literature for the optimal design of heat exchanger networks. Typical optimal criteria are maximum energy recovery and minimum heat-transfer area. However, the heat integration of process streams can lead to process structures that are difficult to control. In this work, a heat exchanger network controllability index is proposed as a measure of heat exchanger network controllability. This controllability index can be calculated easily, making it quite appropriate for use at the conceptual design stage of a chemical process. A case study is presented in which the controllability index is used to compare the controllability characteristics of different networks and also to identify the tradeoffs between controllability and heat integration.