As with any profession, it is important for the volunteer management community to have established ethics and principles – not only for how we work with volunteers but all of our constituencies, including staff colleagues, funders, board members, and, just as importantly, each other as a professional community.
One of the primary documents on ethics in volunteer management, "Professional Ethics in Volunteer Administration," was developed by the former Association for Volunteer Administration; you can read it here (PDF) on the Council for Certification in Volunteer Administration website.
Many of us live in increasingly litigious societies. Whether you see this as a good thing or a bad thing, the fact remains that volunteer management professionals increasingly must be aware of the legalities of their work, whether that is the risks organizations can pose to volunteers or the liabilities volunteers can pose to the organization and/or its constituents. Here are some resources on the legal issues in working with volunteers; where country-specific, we've indicated the source country after the title and author.