Poly(ADP-ribose)polymerase-1 (PARP-1) catalyzes the polymerization of ADP-ribose units from NAD+ modules on target proteins, resulting in the attachment of linear or branched polymers. PARP-1 and its product poly(ADP-ribose)--PAR have recently received considerable attention because of their involvement in a wide range of cellular processes including chromatin modification, metabolism of nucleic acids, transcription regulation, and cell death. This review summarizes recent work on modular structure of six functional domains (A-F) of PARP-1 molecule in the context of three classic domains, i.e., DNA binding (DBD), automodification (AD) and catalytic (CD) released by proteolytic enzymes. A special attention is paid to subcellular localization and molecular mechanisms of PARP-1 posttranslational modifications, such as: poly(ADP-ribosylation), phosphorylation, acetylation and sumolyation. In addition, main functions of PARP-1 are discussed, focusing on the activity of this enzyme in DNA damage detection and repair, genome stability, and cell death.