What Are the Documentation Requirements?

The short answer is: not a lot, and they are not onerous.

In a nutshell, you must have:

I deliberately list them in that order, because it is clearer than the reverse order presented in the Standard. So if someone tells you you have 'write everything down' for an ISO 9001, they're wrong.  Likewise, that tired old 'write what you do and do what you say' mantra.  They may still be operating from experience with previous versions of the Standard, and not be up to date with the much reduced requirements in the current one (2015).

The current version of the Standard ISO 9001: 2015 made big changes in the requirements for documentation. Whereas the version it replaced (2008) still dictated a requirement for a quality manual and written procedures in 6 areas, these have now been dropped.

There is much (mis) information being propagated, including the complete falsehood of 'now we don't need to have any documents at all'! Not true. 

The changes have been very positive in my view, with the aim of making the standard even more flexible, and putting the decision back into the hands of organisations to decide what they need.  For some companies, that might mean a lot of procedures and policies.  For others, it might mean few to even none. It always depends on a number of issues, not least the field in which you operate, the kind of people who work in the organisation (in general, the more highly competent your people are, the less there's a need for a lot written procedures)

Naturally, there is plenty of guidance and simple examples of how to meet the requirements in a practical and simple way in the DIY ISO 9001 Kit.  Or, if you haven't yet made the transition to the 2015 version, there is practical, clear and concise guidance in the DIY Transition Kit

ISO has also published a Guidance document which is worth reading, but only once you've got a bit of a handle on what the Standard is and what its requirements are.