Since someone asks at least once a week, I figured I should state it here and pin it to the top of this forum.
If you are querying fiction:
- You DO NOT need a bio.
- You SHOULD include publishing credits and relevant degrees.
- You SHOULD include writing awards IF it's a large enough competition for an agent to care.
- You CAN include particular expertise relevant to your novel (i.e., a nurse writing a medical thriller).
- If an agent INSISTS on a bio and you have none of the above, give ONE interesting sentence about yourself.
If you are querying non-fiction:
- You DO need a bio.
- You MUST include qualifications—why are you the guy/gal to write this book? What makes you an authority?
- You MUST have a platform—blog following with significant numbers, speaking engagements, etc.
- If you're querying a memoir, go back up to the "fiction" section. Memoirs follow the fiction procedure most of the time, and let's face it—your whole query is your bio.
I hope that covers most of the basic questions. If there are stranger situations that need addressing, post below. Let's keep it all in one place for posterity.