Talk at Pycon 2011 India by - Chetan Vishal. Summary Benefit of multi-threaded application grows with ubiquity of multi-core architecture that potentially can simultaneously run multiple threads of execution. Python supports multi-threaded applications and developers are flocking to realize the assured gain of multiple cores with threaded applications. Unfortunately, Python has significant bottleneck for multi-threading. Any thread in CPython interpreter requires a special lock (GIL) which results in serial, rather than parallel execution of multi-threaded applications, irrespective of cores availability and design techniques. This talk focuses on the problem, dissects the root cause and its implications. The problem alleviation is discussed with introduction of Python3.0 which has new GIL implementation, improving the overall performance of Python threads.