Federal Habeas Corpus in a Nutshell

Newcomers to the capital punishment controversy may be puzzled by ubiquitous references to the common law writ of habeas corpus. What, you may ask, does the Great Writ have to do with the death penalty? The answer is: virtually everything. The lower federal courts have no ordinary appellate jurisdiction to review state criminal judgments for error. They adjudicate federal constitutional claims in death penalty cases primarily by entertaining habeas corpus petitions from death row prisoners. But for federal habeas corpus, capital sentences imposed for state criminal offenses would be examined only in state court and, occasionally, in the Supreme Court (which does, of course, have appellate jurisdiction to review state judgments for federal error)