Systems that require maintenance typically consist of multiple components. In case of economic dependencies, maintaining several of these components simultaneously can be more cost efficient than performing maintenance on each component separately, while in case of redundancy, postponing maintenance on some failed components is possible without reducing the availability of the system. Condition-based maintenance (CBM) is known as a cost-minimizing strategy in which the maintenance actions are based on the actual condition of the different components. No research has been performed yet on clustering CBM tasks for systems with both economic dependencies and redundancy. We develop a dynamic programming model to find the optimal maintenance strategy for such systems, and show numerically that it can indeed considerably outperform previously considered policies (failure-based, age-based, block replacement, and more restricted (opportunistic) CBM policies). Moreover, our numerical investigation provides insights into the optimal policy structure. Binary variable indicating whether or not a replacement (preventive or corrective) should be performed on component i Deterioration parameter of component i Cost of a corrective replacement on component i Cost of a preventive replacement on component i, c p i < c c i Fixed set-up cost for maintenance Optimum cumulative cost from period t on Pdf of the deterioration increments of component i Number of components in the system that need to function for the system to function Fixed failure level of component i Number of components in the system Penalty for a system failure System reliability, given deterioration levels of x 1 , x 2 , … , x N for components 1 , 2 , … , N , respectively Reliability of component i, given a deterioration level of xi Set of all component labels, S N : = { 1 , 2 , … , N } Condition of component i at time t, X 0 i = 0 Condition of component i after possible maintenance has been performed Increase in deterioration on component i during t, X t + 1 i = X ¯ t i + Y t i 
Clustering condition-based maintenance for systems with redundancy and economic dependencies