Gels are the aqueous colloidal suspensions of the hydrated forms of insoluble drugs. A gel is a solid, jellylike material that has properties ranging from soft and weak to hard and tough. Gels are defined as a substantially dilute cross-linked system, which exhibits no flow when in the steady state. Gels are mostly liquid, but they behave like solids due to their three-dimensional cross-linked network within the liquid, which gives them their structure and contribute to their stickiness. Examples are aluminum hydroxide gel, aluminum phosphate gel, and milk of magnesia. Gels are classified as hydrogel or aquagel, organogel, and xerogel.