There are at least three possibilities:

1. Inventor, if the patent is at most partially unassigned (whether or not licensed).
2. Assignee, if the patent is at least partially assigned (whether or not licensed).
3. Licensee, if the patent is licensed. (whether assigned or unassigned)

If the assignment is partial (e.g. to a field, product or territory) or the license is partial, there may be more than one of the three capable of suing if the alleged infringement affects more than the assigned or licensed part. It is possible all 3 might join the suit as plaintiffs. And, the two or three can have separate attorneys to protect their separate interests, as a licensee might have a cause of action against a patent owner who failed to enforce a licensed patent and such failure materially damages the licensee. Often the license or assignment will, particularly if it is well drafted, contractually determine who has the right and/or duty to sue for infringement.

There might also be situations where a distributor or retailer, particularly an exclusive one, might have standing to sue if the Inventor, Assignee and Licensee chose not to take action against an infringer. In such a situation the distributor or retailer might also take action against the patent owner for failure to enforce the patent.

There are at least three possibilities:

1. Inventor, if the patent is at most partially assigned (whether or not licensed).
2. Assignee, if the patent is at least partially assigned (whether or not licensed).
3. Licensee, if the patent is licensed. (whether assigned or unassigned)

If the assignment is partial (e.g. to a field, product or territory) or the license is partial, there may be more than one of the three capable of suing if the alleged infringement affects more than the assigned or licensed part. It is possible all 3 might join the suit as plaintiffs. And, the two or three can have separate attorneys to protect their separate interests, as a licensee might have a cause of action against a patent owner who failed to enforce a licensed patent and such failure materially damages the licensee. Often the license or assignment will, particularly if it is well drafted, contractually determine who has the right and/or duty to sue for infringement.

There might also be situations where a distributor or retailer, particularly an exclusive one, might have standing to sue if the Inventor, Assignee and Licensee chose not to take action against an infringer. In such a situation the distributor or retailer might also take action against the patent owner for failure to enforce the patent.

So, there might be different plaintiffs for different defendants. Choice of desired forum might have a bearing on who is chosen to sue. Patent litigation can get very complicated very quickly, and this is just about who sues who.

There are at least three possibilities:

1. Inventor, if the patent is at most partially unassigned (whether or not licensed).
2. Assignee, if the patent is at least partially assigned (whether or not licensed).
3. Licensee, if the patent is licensed. (whether assigned or unassigned)

If the assignment is partial (e.g. to a field, product or territory) or the license is partial, there may be more than one of the three capable of suing if the alleged infringement affects more than the assigned or licensed part. It is possible all 3 might join the suit as plaintiffs. And, the two or three can have separate attorneys to protect their separate interests, as a licensee might have a cause of action against a patent owner who failed to enforce a licensed patent and such failure materially damages the licensee.

There might also be situations where a distributor or retailer, particularly an exclusive one, might have standing to sue if the Inventor, Assignee and Licensee chose not to take action against an infringer. In such a situation the distributor or retailer might also take action against the patent owner for failure to enforce the patent.

There are at least three possibilities:

1. Inventor, if the patent is at most partially unassigned (whether or not licensed).
2. Assignee, if the patent is at least partially assigned (whether or not licensed).
3. Licensee, if the patent is licensed. (whether assigned or unassigned)

If the assignment is partial (e.g. to a field, product or territory) or the license is partial, there may be more than one of the three capable of suing if the alleged infringement affects more than the assigned or licensed part. It is possible all 3 might join the suit as plaintiffs. And, the two or three can have separate attorneys to protect their separate interests, as a licensee might have a cause of action against a patent owner who failed to enforce a licensed patent and such failure materially damages the licensee. Often the license or assignment will, particularly if it is well drafted, contractually determine who has the right and/or duty to sue for infringement.

There might also be situations where a distributor or retailer, particularly an exclusive one, might have standing to sue if the Inventor, Assignee and Licensee chose not to take action against an infringer. In such a situation the distributor or retailer might also take action against the patent owner for failure to enforce the patent.