Why don't I see a certain field as an option when creating a list of my Leads or Contacts?

When creating a new query to build a list, Leads will have Lead and Owner fields and Contacts will have Contact, Account and Owner fields as query options.
 
If you don't see a field that you need to reference in your query you can also run a Salesforce Report, add the results to a Salesforce Campaign, and create a list from the Campaign members. If you have access to the Salesforce Campaign object you will see this option when you create a new list.