Embodiments described herein provide apparatus and methods for performing HARQ operations using parallel HARQ threads, where each new transmission of a MPDU/A-MPDU/PSDU triggers the activation of a HARQ thread. Each HARQ thread contains one or more HARQ coding words or coding units. A HARQ thread index is setup by a transmission opportunity (TXOP) holder for a corresponding PSDU and is used to identify HARQ threads. Multiple HARQ threads can be aggregated into one PPDU for transmission (or retransmission). The maximum number of HARQ threads can be negotiated between AP and non-AP STAs based on buffer requirements, for example. A HARQ thread can end when all MPDUs associated with the HARQ thread have been decoded or other predetermined conditions are met.