BASIC-PLUS is an extended dialect of the BASIC programming language that was developed by Digital Equipment Corporation (DEC) for use on its RSTS/E time-sharing operating system for the PDP-11 series of 16-bit minicomputers in the early 1970s through the 1980s.

BASIC-PLUS was based on BASIC-8 for the TSS/8, itself based very closely on the original Dartmouth BASIC. BASIC-PLUS added a number of new structures, as well as features from JOSS concerning conditional statements and formatting. In turn, BASIC-PLUS was the version on which the original Microsoft BASIC was patterned.

Notable among the additions made to BASIC-PLUS was the introduction of string functions like MID$ and LEFT$, in addition to Dartmouth's original all-purpose CHANGE command. In future versions of the language, notably Microsoft's, CHANGE was removed and BASIC-PLUS's string functions became the only ways to perform these sorts of operations. Most BASICs to this day follow this convention.

The language was later rewritten as a true compiler as BASIC-Plus-2, and was ported to the VAX-11 platform as that machine's native BASIC implementation. This version survived several platform changes, and is today known as VSI BASIC for OpenVMS.