Vedic is the earliest form of Sanskrit, being the language in which the Vedas were written. The oldest text is the Rig Veda (Rg Veda), which seems to date from a little before 1000 BCE. It was spoken in north-western India, before the Aryan people had spread far and wide over the Indian subcontinent. (However, see Aryan invasion theory for doubts over this traditional dating for the migration.)

Vedic Sanskrit differs from Classical Sankrit, the prestige language codified by the grammarian Panini at an unknown date, perhaps around 300 BCE. From Panini's time Sanskrit was only a literary/theological/philosophical medium, not a living language of the people: by then they spoke Prakrit in the various dialects that gave rise to modern Indian languages. Prakrits are phonetically much simplified compared to their ancestral Sanskrit; however, Vedic Sanskrit and Classical Sanskrit do not differ greatly.

Some scholars insist that Vedic is not a form of Sanskrit, and that 'Vedic Sanskrit' is a contradiction in terms. To them Sanskrit means precisely Classical Sanskrit, and it and Vedic are forms of Old Indian.

One important phonological difference is that Vedic had a pitch accent, which could be on any syllable, and corresponded to the pitch accent in its ancestor, Proto-Indo-European, and in its cousin Classical Greek, and which is still found in Lithuanian. (A few archaic features like this give rise to the erroneous story that Lithuanian and Sanskrit are similar.) In Classical this was replaced by a stress accent, on a non-final syllable that was predictable by counting long vowels and consonant clusters.

There was some alternation of l and r. The English light (in weight) = Latin levis corresponds to Classical laghu, but the Vedas use raghú, as does the closely-related Iranian branch.

In the o-stems, such as áçvas 'horse', corresponding to the familiar Latin equus and Greek hippos, the nominative singular ending is -as, which classically is -ah. The instrumental was long , later -ena. The genitive plural was -âm (later replaced by -ânâm), corresponding to Greek -ôm.

There was no uninflected infinitive as such: in later Sanskrit the form found in bhártum 'bear' was regularized as the infinitive.