The great tit is large for a tit at 12.5 to 14.0 cm in length, The Great Tit has a bluish-black crown, black neck, throat, bib and head, and white cheeks and ear coverts. The breast is bright lemon-yellow and there is a broad black mid-line stripe running from the bib to vent. There is a dull white spot on the neck turning to greenish yellow on the upper nape. The rest of the nape and back are green tinged with olive.

The great tit is, like other tits, a vocal bird, and has up to 40 types of calls and songs. The male is much more vocal and the female rarely calls. Soft single notes such as "pit", "spick", or "chit" are used as contact calls. A loud "tink" is used by adult males as an alarm or in territorial disputes.

Great tits are primarily insectivorous in the summer, feeding on insects and spiders. Their larger invertebrate prey include cockroaches, grasshoppers and crickets, lacewings, earwigs, bugs (Hemiptera), ants, flies (Diptera), caddis flies, beetles, scorpion flies, harvestmen, bees and wasps, snails and woodlice. During the breeding season, the Great tits prefer to feed protein-rich caterpillars to their young.