Sustainable growth and the commercial success of "Mainport Holland", located in one of Europe’s most densely populated areas, is threatened by a lack of available land, a congested infrastructure, and an increasingly complex social, economic and political reality. To deal with these threats mainports, such as the Port of Rotterdam, are reengineering their planning processes. Instead of making plans based on an extrapolation of current trends, the aim is now to find answers to what-if questions which are applied to concurrent scenarios. Mainport planning is like solving a large jigsaw puzzle, but unlike a jigsaw puzzle the pieces used to solve the puzzle are not available beforehand, and there is no single best solution. Solving the mainport planning puzzle is a difficult, lengthy, knowledge and information intensive, multi- actor process. The challenge is to support invoking the memory and the creativity of multiple actors, with different objectives, that are specialized in different fields of knowledge, and that work in different contexts, such that effective mainport planning can be conducted. Adhering to the concept of studios, suites and services as introduced by Keen and Sol (2007), we introduced the design of a Mainport Planning Suite (MPS), i.e. a suite of services to support the actors in a studio-based planning process and improve their effectiveness in mainport planning. Following a design science strategy, we designed our MPS in an iterative way. First we studied mainport planning in practice in two exploratory case studies. From the exploratory case studies we found that supporting mainport planning should be focused on visualizing the knowledge and information that is used and produced during a mainport planning process. Based on the principles of visualization found in literature, we constructed a framework that we used to identify technology building blocks and requirements to design and implement an MPS. Based on the identified requirements we chose to design our MPS as a suite of loosely coupled services that are provided by a web portal. The main services provided by our suite are Map, Sketchbook, Matchbox, and Aspect Explorer, which support analysis, design, evaluation and choice in mainport planning. These services are supplemented with a number of services that support the process of planning, e.g. action lists, decision lists and project information services. The MPS was evaluated in two evaluation sessions at the Port of Rotterdam. For each evaluation session a prototype was assembled from the MPS services. During the first evaluation session a team of area planners was invited to participate in a fictive studio-based area planning meeting supported by our suite. Not all functionality was available during first evaluation session; therefore a second evaluation session was organized in which we used structured walkthroughs of an improved prototype. Based on the outcomes of the evaluation sessions, it is our strong conviction that an MPS is potentially useful and usable to improve the effectiveness of studio-based mainport planning. Future research might focus on the integration of simulation models in an MPS, the extent to which an MPS can support the automatic reporting of planning outcomes, the design of an approach for using an MPS, and the extent to which an MPS can be used in spatial planning in general.