What are teams?
Trello offers the option to create teams, and to set your boards so that they belong to those teams. Just like boards, teams can have members (including team admins and normal team members). There are no limits to the number of members you can have in a team, or the number of teams you can belong to in a single account.
Should I use a team for my project?
If you're in a situation where you've got multiple, related boards, a team is probably going to be a good idea. This is particularly useful if you're a company (or a team within a company) who uses boards for different aspects of your workflow.
The team provides a helpful way to see all of your boards in one place, and track all of your members in one place. We usually recommend that teams encompass a group, or a company, rather than a single project—projects are best handled as a board or boards.
For free teams (those that haven't upgraded to Business Class), being a team admin doesn't give admin control over team boards—to make changes to other users' boards in your team, you'll need to be invited as a board admin manually. Instead, the main benefit for teams at that level is to keep everything in one place in the app—team-visible boards can all be seen on one page, which is helpful for new team members.
For Business Class teams, team admins also have admin control over any board in the team itself, without needing to be invited by the board's admin.
Upgrading to Business Class will give team admins control over boards in that team, as well.
Should I have multiple teams for my company?
If you're a large organization with multiple discrete business units, setting up separate teams may be a good option. You'll also want to check out our Enterprise plan if you're considering purchasing Trello Business Class.
If you're simply looking for a way to group boards together, we would recommend using a single team and then using board Collections to organize them. Board collections are a feature of Business Class, which you can read about here.
If you decide to upgrade to Business Class, It's much easier (and more cost effective) to upgrade a single team to Business Class than to have to upgrade multiple teams.
Upgrading to Business Class
Business Class upgrade happens per-team, rather than per-individual-account, which is why we suggest trying to organize your boards and members into a single team. Business Class provides lots of additional features, such as integrations with other services, collections, and a host of features to make it easier to manage your team.
If you do need to maintain several teams for your company, you may be interested in our Enterprise plan. One of the features of Enterprise is that you only pay one time for each unique member, regardless of how many teams they belong to. More information about that plan is covered on that page.