Nairobi has a serious restaurant scene, particularly in Westlands and Karen. The city's cosmopolitan population means Indian, Chinese, Japanese, Lebanese, and Ethiopian food are all available to a standard well above what you'd find in most East African cities.
For cheap Kenyan street food, look for hotelies (small local restaurants) serving ugali (stiff maize porridge), nyama choma (grilled goat or beef), sukuma wiki (collard greens), and githeri (beans and maize). A full meal costs under KSh 200. Choose one that is busy at mealtimes — the food turns over quickly and is always fresh.
Notable restaurants include the Carnivore (game meats on swords, a genuine institution), Tamarind (Swahili Coast seafood), Java House (the city's reliable café chain), About Thyme (garden restaurant in Lavington), and Tamambo (Karen outdoor terrace).