"Federal habeas corpus as we know it is by and large a procedure under which a federal court may review the legality of an individual's incarceration. It is most often invoked after conviction and the exhaustion of the ordinary means of appeal. It is at once the last refuge of scoundrels and the last hope of the innocent. It is an intricate weave of statute and case law whose reach has flowed and ebbed over time. Current federal law operates under the premise that with rare exceptions prisoners challenging the legality of the procedures by which they were tried or sentenced get 'one bite of the apple.' Relief for state prisoners is only available if the state courts have ignored or rejected their valid claims, and there are strict time limits within which they may petition the federal courts for relief. Moreover, a prisoner relying upon a novel interpretation of law must succeed on direct appeal; federal habeas review may not be used to establish or claim the benefits of a 'new rule.' Expedited federal habeas procedures are available in the case of state death row inmates if the state has provided an approved level of appointed counsel. The Supreme Court has held that Congress enjoys considerable authority to limit, but not to extinguish, access to the writ."
CRS Report for Congress, RS22432
Federation of American Scientists: http://www.fas.org/main/home.jsp