Structural isomerism

In structural isomers, the chemical formula remains the same but the structural formula changes.
Position isomerism occurs when the location of the functional group varies in each isomer.
Functional group isomerism occurs when there are different functional groups present.
Chain isomerism occurs when isomers differ in the structure of their carbon 'skeleton'.

Stereoisomerism

Stereoisomers are compounds whose molecules have the same atoms bonded to each other, but with different arrangements of the atoms in space.
Geometrical (cis/trans) isomerism occurs due to the restricted rotation about a C=C double bond. In cis isomers, the substituents are on the same side of the double bond, while in trans isomers, they are on opposite sides.
Optical isomerism occurs when a molecule contains a carbon atom bonded to four different atoms or groups of atoms. This carbon atom is called a chiral centre. The two isomers, called enantiomers, are mirror images of each other and cannot be superimposed.