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Collateral Estoppel
Collateral estoppel prevents a person from relitigating an issue that was already decided in a previous lawsuit, even if the new case involves a different claim.
What it actually is
It is a legal doctrine that bars re-arguing a specific fact or legal question that was actually litigated and necessarily decided in an earlier proceeding. It typically arises when a party tries to raise an issue in a second case that was already resolved against them in a prior case, assuming the issue was essential to the earlier judgment and the party had a full opportunity to contest it.
Why it matters in your case
If you lost on a key fact in an earlier lawsuit, you cannot bring that same fact up again in a later lawsuit against the same opponent. This saves court time and prevents inconsistent rulings, so you must accept that fact as settled even if your new case involves different legal theories.
The common misunderstanding
People often confuse collateral estoppel with res judicata: res judicata bars entire claims that were or could have been brought, while collateral estoppel only bars specific issues that were actually decided. Also, some think it applies only to the same parties, but in some situations it can also bind or benefit non-parties (though this varies by jurisdiction).
Get the actual rule
Definitions are orientation; rules are authority
This page explains the concept. When it matters to your case, read the rule that governs it in your court — we hold Texas, federal and Washington court rules word for word, and every state's official resources are on the state pages. If someone cites a case at you, check that it exists first.
Related
Terms that travel with this one
General explanation, not legal advice, and not specific to any state — procedures and deadlines vary by jurisdiction and court. If you can get a lawyer or free legal aid, do: every real option.