BGP routing table sizes have increased by an order of magnitude over the last six years. This dramatic growth can decrease packet forwarding speed and demand more router memory space. We explore the extent that various factors contribute to the routing table size and characterize the growth of each contribution. We begin with a measurement study using the routing tables of an Oregon route views server to determine the contributions of multi-homing, load balancing, address fragmentation, and failure-to-aggregate to routing table size. Address fragmentation makes the greatest contribution and it is three times those of multihoming or load balancing. The contribution of failure-to-aggregate is the least. Although multihoming and load balancing contribute less to routing table size than address fragmentation, we observe that their contributions grow faster than the routing table does and that load balancing has surpassed multihoming, becoming the fastest growing contributor. Moreover, we find that both load balancing and multihoming contribute to routing table growth by introducing more prefixes of length between 17 and 25, which are the fastest growing prefixes. Next, we examine the growth routable IP addresses, and conclude that their growth is much slower than that of routing table size. Lastly, we demonstrate that our findings based on views derived from the Oregon server are accurate through an evaluation using 15 additional routing tables collected from different locations in the Internet.