Basics
Tawheed
The oneness of Allah
التوحيد
Tawheed (tawḥīd) is the affirmation of the absolute oneness of Allah. It is the first thing a Muslim believes and the lens through which everything else is understood. The Prophet (peace and blessings be upon him) was sent to call people back to this single truth.
Three sides of the same diamond
Scholars describe tawheed in three categories so it can be studied clearly. They are not three different beliefs; they are three windows on one truth.