This work presents a decision-making framework for the design and retrofit of sensor networks, as well as a general strategy for the correlation of the cost and performance of the different sensor arrangements (number, placement) that can be systematically analyzed. The analysis of the steps required to solve the sensor placement problem for design or retrofitting cases implies the identification of the information flows involved. Such a conception allows for the modular design of a tool for computer-aided sensor network design/retrofitting. An interface specification is proposed for this tool, and a prototype is developed for validation purposes. The decision-making strategy adopted is independent of the particular algorithms and procedures used. Hardware redundancy, steady-state/dynamic processes, design/retrofitting, and a catalog of different available sensors are all taken into account, thus leading to a generic framework that is able to follow the future trends of sensor placement. Seeking the synergy given by reusability and standardization, the sensor placement tool has been developed following the CAPE-OPEN (CO) guidelines, allowing for the integration of other software modules such as those for process modeling and data reconciliation.