Many women have served in frontline support roles such as medics and bomb disposal experts for years now, but up until 2016, they were banned from serving in close combat roles.
It wasn't until former Prime Minister David Cameron lifted the ban allowing women to enter the cavalry, infantry and armoured corps. But this was to be phased in slowly.
According to the latest Ministry of Defence (MOD) figures, women make up 10.4% of regular forces.
When the lifting of the ban began, women were able to join some parts of the Royal Armoured Corps in 2016 - they now have 35 women serving.
The RAF was the first to open all roles up to women.
From 1 September 2017, women were able to join the RAF Regiment, the air force's ground fighting force for protecting air bases.
Up until Gavin Williamson's announcement on Thursday, women have not been able to join the infantry, which completes the final phase.
But it hasn't always been easy for women to join the Armed Forces...
Dating back to the 17th century, some women fought in wars. However, this was only possible if they had a good disguise because the reality was that women were only allowed to join as a nurse.
For the first time in the First World War, due to the heavy losses of the Battle of Somme, women were able to work in supporting roles so men could be freed up for combat.
However, it wasn't until 1941 that the National Service Act made the conscription of women legal.
From 1949 to its disbandment in 1992, women worked in the Women's Royal Army Corps in support and medical positions.
Women have also been serving in the Navy and the RAF for over 100 years after the Women's Royal Naval Service and the Women's Royal Air Force were formed in 1917 and 1918 respectively.
Women on the frontline elsewhere in the world
Ground combat roles are already open to women in a number of countries around the world.
Women serving in combat roles on the frontline is nothing new to
In Denmark, female soldiers have been fighting on the frontline since 1988. According to a 2010 British MOD study of the Danish, women performed just as well as men in land combat roles.
Women serving in combat roles on the frontline is also nothing new to New Zealand, with no restrictions on women serving in the military since 2001.
In America, women have been able to fight on the frontline since 2015, with the first US female marine qualifying in 2017.
The recruitment process for female Royal Marines in the UK has now got underway.
Similarly, in Canada women have been allowed to serve in frontline combat roles since January 2013.