All Aes Sedai except the Amyrlin Seat belong to an Ajah. Each follows a specific philosophy of the use of the One Power and the purposes of the Aes Sedai. There are seven official Ajahs, each designated by a color. The eighth, unofficial Ajah, is the Black Ajah (spoilers).
Each Ajah has its own organization and communications network including a spy network called the "eyes-and-ears". Curiously, the head of each Ajah is a closely guarded secret within the Ajah and the Ajah head is typically not a Sitter.