This article is from the Amiga FAQ, by Ignaz Kellerer with numerous contributions by others.
You need the `ADSP' (Amiga Developer Support Program) documents. To get this write a letter to your local Commodore branch asking for these documents. Everything else should be explained there. The german address (for the US address see CATS) is Commodore Lyoner Strasse 38 60528 Frankfurt There are three different developer versions: *Registered* developers get access to the CBMNET (kind of a Commodore-internal Usenet), which makes it possible to discuss problems with other developers, Commodore engineers included. Registered developers pay about US$80 per year, plus initial US$30 initially.
*Certified* developers seem to me the most interesting claass: They have the possibility copy the most beta versions of the system software (Kickstart and Workbench) and the respective Includes and AutoDocs. (Not all beta versions and especially no beta hardware.) You pay about US$250 per year plus US$50 initially for this.
*Commercial* developers finally have in most details the same as certified developers, but may expect to get more beta versions and sooner, included beta hardware (This has *not* always been so in the past.), hencethey pay about US$400 plus US$50 initially.
The above describes the prices and the situation in Germany and might be different elsewhere. Especially not all Commodore branches offer the registered status. A hint is to build a group of users and become a developer group, so the costs are reduced.
All developers have to sign non-disclosure agreements (`NDA') which specify that we may not discuss information outside of authorized areas even to other developers until given explicit permission by Commodore.