The particles of the Proto-Indo-European language (PIE) have been reconstructed by modern linguists based on similarities found across all Indo-European languages.

Many particles could be used both as adverbs and postpositions. This is similar to modern languages; compare English He is above in the attic (adverb) and The bird is above the house (preposition). The postpositions became prepositions in the daughter languages except Anatolian, Indo-Iranian and Sabellic; some of the other branches such as Latin and Greek preserve postpositions vestigially.

Reflexes, or descendants of the PIE reconstructed forms in its daughter languages, include the following.

Untranslated reflexes have the same meaning as the PIE word.

In the following languages, two reflexes separated by a slash mean:

Two privatives can be reconstructed, *ne and *mē, the latter only used for negative commands. The privative prefix *n̥- is likely the zero grade of *ne.

Adverbs derived from adjectives (like English bold-ly, beautiful-ly) arguably cannot be classified as particles. In Proto-Indo-European, these are simply case forms of adjectives and thus better classified as nouns. An example is *meǵh₂ "greatly", a nominative-accusative singular.

The following conjunctions can be reconstructed: