S/PDIF (Sony/Philips Digital Interface) is a type of digital audio interconnect used in consumer audio equipment to output audio over reasonably short distances. The signal is transmitted over either a coaxial cable with RCA connectors or a fibre optic cable with TOSLINK connectors. S/PDIF interconnects components in home theatres and other digital high-fidelity systems.

S/PDIF is based on the AES3 interconnect standard. S/PDIF can carry two channels of uncompressed PCM audio or compressed 5.1/7.1 surround sound (such as DTS audio codec); it cannot support lossless surround formats that require greater bandwidth.

S/PDIF is a data link layer protocol as well as a set of physical layer specifications for carrying digital audio signals between devices and components over either optical or electrical cable. The name stands for Sony/Philips Digital Interconnect Format but is also known as Sony/Philips Digital Interface. Sony and Philips were the primary designers of S/PDIF. S/PDIF is standardized in IEC 60958 as IEC 60958 type II (IEC 958 before 1998).

A common use for the S/PDIF interface is to carry compressed digital audio for surround sound as defined by the standard IEC 61937. This mode is used to connect the output of a DVD player or computer, via optical or coax, to a home theatre amplifying receiver that supports Dolby Digital or DTS. Another common use is to carry two channels of uncompressed digital audio from a CD player to an amplifying receiver.

S/PDIF was developed at the same time as the main standard, AES3, used to interconnect professional audio equipment in the professional audio field. This resulted from the desire of the various standards committees to have at least sufficient similarities between the two interfaces to allow the use of the same, or very similar, designs for interfacing ICs.[6] S/PDIF remained nearly identical at the protocol level,[a] but changed the physical connectors from XLR to either electrical coaxial cable (with RCA connectors) or optical fibre (TOSLINK; i.e., F05 or EIAJ optical), both of which cost less than the XLR connection. The RCA connectors are typically colour-coded orange to differentiate from other RCA connector uses such as composite video. The cable was also changed from 110 Ω balanced twisted pair to 75 Ω coaxial cable, using RCA jacks.

Signals transmitted over consumer-grade TOSLINK connections are identical in content to those transmitted over coaxial connectors, though TOSLINK S/PDIF commonly exhibits higher jitter.