BBC has the Article 50 withdrawal notification letter here. Not surprisingly, it does not tell us much about how the withdrawal talks will go (the UK would like a "deep and special partnership" with the EU).
The substance of the negotiations will become more clear as we move along. The folks at ECIPE are kicking things off with a seminar that looks at whether CETA offers a model for the EU-UK agreement:
Is CETA a good model for a future EU-UK trade agreement after Brexit?
Today is the day Theresa May triggers Article 50. This day marks the beginning of a divorce process without precedence in the history of the EU. Contrary to other policy areas trade policy is an area where the EU has a longstanding negotiating experience and different model agreements to revert to. One agreement which could serve as a model agreement for a post-Brexit trade agreement between the EU-27 and the UK is CETA, the Comprehensive Economic and Trade Agreement between the EU and Canada. CETA is the latest and most comprehensive trade agreement signed between the EU and a large, highly-developed economy.
But is CETA really a good model for a future EU-UK trade agreement? Would a CETA-type agreement be suitable for the interests and priorities of the EU-27 and UK? Is CETA an agreement which is deep enough to minimize negative economic impacts on the EU-27 and UK economies? What are lessons learned from the negotiation and conclusion of CETA?
In response to their main question, I would say no. CETA may offer a few things here and there to help guide the UK-EU talks, but by and large it is not a good model for the UK and EU to follow. For one thing, it leaves quite a few tariffs in place. For another, it has a lot of provisions that are completely unnecessary for the UK-EU trade relationship (investment protection, or labor and environment rules).
If I were involved in the UK-EU talks, I wouldn't focus on any single existing trade agreement as a general model. Rather, I would think about what issues should be covered and in what way, and then look around to see how various other agreements have dealt with them.