Multipath TCP, a major extension to regular TCP, allows TCP clients to utilize multiple paths to improve the transfer rate and connection robustness. Providing these benefits without requiring to upgrade network infrastructure nor applications, Multipath TCP is becoming more popular. Notably Apple iOS 7 now supports it for SIRI. However, there is still lack of a complete understanding of Multipath TCP in practice. How much can a user benefit from Multipath TCP in different scenarios? Which factors affect the performance of Multipath TCP? How well can we predict the behavior of Multipath TCP in a specific environment? Our research aims to answer these questions by large-scale measurements and model-based analysis. The answers will be an important input for designers and developers to further improve Multipath TCP.