Governments around the world are investing significant resources in the development and expansion of logistics clusters. This dissertation analyzes the cluster phenomenon focusing on four topics. First, it develops a methodology to identify clusters and applies it to the context of the US. By analyzing the case of logistics clusters, this thesis contributes to a more general debate in the industrial clusters literature: while many authors see industrial clusters growing, others see them dispersing. Evidence of increasing concentration of the logistics industry in clusters in the US over time is tested and documented. In addition, some evidence that logistics activities in counties inside clusters show higher growth than in counties outside clusters is found. Second, this thesis studies the relationship between freight accessibility and logistics employment in the US. It develops an accessibility measure based on a gravity model, focusing on four different modes of transportation: road, rail, air, and maritime. Using a Partial Least Squares model, these four different freight accessibility measures are combined into two constructs, continental and intercontinental freight accessibility, and then analyzed against logistics employment. Results show that highly accessible counties attract more logistics employment than other counties. The analyses also show that it is important to control for the effect of population, since it explains the most variation in the logistics employment across counties. Third, this dissertation also analyzes the benefits of logistics clusters, possibly explaining their continuous growth and wide popularity among both private agents and policy makers during the last decade. Using interview data and grounded theory, four major driving forces that may explain their growing presence are identified: collaboration, value added services, upward mobility and job creation at different levels. Finally, using a quantitative approach this thesis analyzes two major effects of agglomeration on firms located within logistics clusters: more collaboration and the provision of more value added services. Using survey data and structural equation modeling these hypotheses are tested using information from the Zaragoza (Spain) Logistics Cluster. The results show that companies located in logistics clusters do collaborate more and offer more value added services than companies that are not agglomerated.