As the marijuana industry expands, the financial opportunity the market can offer investors like Peter Thiel and big corporations like Microsoft gets a little more apparent. This week, thousands of people and hundreds of businesses will descend upon Oakland, California, for the third-annual National Cannabis Industry Association Business Summit and Expo.

The event, hosted by the industry group at the Oakland Marriott City Center, will feature keynote speeches and workshops by politicians like Gavin Newsom, the lieutenant governor of California, veteran entrepreneurs like Steve DeAngelo, the co-founder of Harborside, one of the largest dispensaries in the U.S., and policy seminars held by lawyers like Bob Hoban, who helped Colorado's first dispensaries open up legally. Entrepreneurs and investors looking to get into the game, which is a $40 billion nation-wide market, will have the opportunity to learn from people who have been doing it for years.

California legalized medical marijuana in 1996 with Proposition 215. This November, the state will vote on whether or not to legalize recreational cannabis. While Colorado, Oregon and Washington have received the bulk of the attention lately with all three states legalizing recreational marijuana, California is thought to be a sleeping giant --the state grows more marijuana than any other in the nation.

Check back on to follow the news and stories coming out of the conference.