An embodiment package includes a first fan-out tier having a first device die, a molding compound extending along sidewalls of the first device die, and a through intervia (TIV) extending through the molding compound. One or more first fan-out redistribution layers (RDLs) are disposed over the first fan-out tier and bonded to the first device die. A second fan-out tier having a second device die is disposed over the one or more first fan-out RDLs. The one or more first fan-out RDLs electrically connects the first and second device dies. The TIV electrically connects the one or more first fan-out RDLs to one or more second fan-out RDLs. The package further includes a plurality of external connectors at least partially disposed in the one or more second fan-out RDLs. The plurality of external connectors are further disposed on conductive features in the one or more second fan-out RDLs.