1.  Psī is the twenty-third letter in the Greek alphabet.

2.  Psī is a compound continuant consonant. Its phoneme is the combination of ī + (unvoiced) sigma. When psī is a word's initial consonant, its phoneme's sound is like "ps" as in "psalms." Its medial or final phoneme's sound is like the "ps: in "lips" or "taps." However, most people do not make this distinction as it is not in Modern Greek.

3.  Psī's capital and small letter look similar. However, the capital letter's stem sits on the base line whereas its small letter's body rests on the base line with its stem dropping below it.

4.  Psī is always transliterated into English with two consonants, "Ps" or "ps."