Python 2 and Python 3 have a number of differences, here are principal ones: 1. **Print statement**: In Python 2, "print" is treated as a statement rather than a function. Python 3 requires parentheses around the items to be printed: print("Hello World"). 2. **Division behavior**: Python 2 performs floor division with the / operator when both operands are of integer type. However, in Python 3, / always performs true division, and // is now used for floor division. 3. **Unicode Support**: Python 2 has ASCII str() types by default, separate unicode(), but no byte type. On the other hand, Python 3 has Unicode (utf-8) strings and a separate bytes type. 4. **Syntax and Libraries**: Python 3 syntax is simpler and easily understandable whereas in Python 2, syntax is comparatively complex. Also, many old libraries don’t work without modification on Python 3. 5. **Error Handling**: In Python 2, there is 'StandardError' which is base class for all built-in exceptions except 'StopIteration' and 'SystemExit'. Python 3 removes 'StandardError', and 'Exception' is base class for all built-in exceptions. 6. **Iteration**: Python 3's range function behaves like Python 2's xrange. They both provide a way to generate a list of integers for you to use, however you please. The main difference is that range returns a Python list object and xrange returns an xrange object. Which one should you use? Python 2 was officially discontinued (end of life) in 2020, so for any new projects it's highly recommended to use Python 3. Developer community and libraries are focused more on Python 3 now, and you'll get better community support for Python 3 and its newer features. This is just the tip of the iceberg. The languages have evolved independently over time, and there are other minor distinctions, most of them under the hood. I'd recommend checking out the official documentation for each version if you're curious, but hopefully this list will give you a ground to start.