With variable pricing, a single seat in a compartment can be sold to different customers at different prices. As we've seen, a particular set of rules and restrictions are associated with each fare product to ensure that it can only be purchased by the market segment that it targets. How many seats should a carrier make available to each different fare product? How do you manage these seat allocations over the booking cycle in response to actual demand? How do you ensure that you reserve enough seats for the last-minute high-revenue customer?Most of the questions above will be addressed in the next module on seat inventory control that immediately follows this one. Booking classes are an integral part of seat inventory control. Before we can discuss the logistics of inventory control we need to understand booking class assignment and structure. We begin in the first section by describing the use of booking classes in a carrier's computer reservation system and their evolution over time. Section 2 looks at the process of assigning different fare products to each booking class and identifies potential problems. In the final section we consider different booking class structures and explain the difference between independent versus nested control structures.