Every year, I give an open talk to the returning students at Harvard Business School on what makes the Boston start-up scene special. I do it for two reasons:  

1. As an advocate for the local innovation ecosystem, I want to make sure all these smart, talented folks from around the world can access and plug in to the amazing local resources available to them.

2. Boston is a microcosm of the ingredients for a successful start-up community, a topic of great interest to policy makers and leaders all over the world (for more on this topic, see Brad Feld's excellent book, StartUp Communities).  

The city of Boston is a relatively small one (the 21st largest city in the US with a population of 600k and a combined metro area that ranks it 10th), yet it is consistently ranked as one of the most innovative clusters in the world.

This presentation gives you a sense of why.

I have written in the past that in the IT sector, Boston suffers from not having more "platform companies", such as Facebook, Google, Twitter, LinkedIn. As the above presentation shows, only a few companies in Boston are of the scale where they are platforms for other startups to plug in to and large enough to create their own industrial clusters. Hopefully, that will change in the coming years.