Expatriates and visitors need to abide by a public dress code in Saudi Arabia. The exception is for those who live within residential compounds with monitored access.
The standard clothes for male expats in Saudi Arabia are trousers and shirts. A non-Saudi wearing a Saudi thobe (a white robe with sleeves) will look odd, and may cause offense. Shorts should never be worn, unless at the gym, beach or hotel pool.
Local and foreign women are all required to wear the abaya, a long and loose black robe over their clothes as well as the hijab (the black head scarf). Without the hijab, women will risk harassment from the religious police (the mutaween). Abayas are sold in shops everywhere, and come in various styles and designs, but only in the color black.