Queen Elizabeth II has reigned since 6 February 1952 

When Elizabeth II succeeded her father in 1952, new stamps were needed. The result was a collection of variations on a theme that came to be known as the Wilding issues, based on a portrait of Queen Elizabeth II by photographer Dorothy Wilding

Wildings were used until 1967, when the Machin issues were introduced on 5th June. 

The Machin design is very simple, a profile of the Queen on a solid colour background, and very popular, still being the standard British stamp as of today. They have been printed in scores of different colours; in addition, decimalisation required new denominations, and there have technical improvements in the printing process, resulting in literally hundreds of varieties known to specialists

Stamps issued to commemorate events relating to the present Royal Family have, during QEII's reign, become a growing trend