Legal and compliance
Regulation D
Also known as Rule 506(b) and 506(c)
The US exemption most private funds use to raise money without registering the offering.
Under Rule 506(b) a manager may not advertise or solicit the general public, and it raises from accredited investors plus a few sophisticated ones. Under Rule 506(c) it may advertise publicly, but every investor must be accredited and the manager must take reasonable steps to verify that. Both need a Form D filing after the first sale.
Why it matters when you raise
Choosing between 506(b) and 506(c) decides how you can market the fund, so make the call before you publish anything.