For Hindus, Sikhs and Jains it's one of the biggest events in the calendar and symobolises the triumph of light over darkness, good over evil. And with at least 20,000 people of Indian descent in Wales, Cardiff will be joining in with the celebrations.
The Wales Millenium Centre in Cardiff Bay will be lit up in the colours of the Indian flag to celebrate along with hosting bollywood dances and Indian street food.
What is Diwali?
Diwali is the Hindu festival of lights.
The festival is observed by Hindus, Sikhs and Jains, with its main theme the triumph of light over darkness and good over evil.
Houses are decorated with candles and colourful lights.
The light symbolises self-improvement and represents new beginnings.
For many, Diwali celebrates the legend of Lord Rama and his wife Sita returning to their kingdom in northern India after their 14 day exile and defeating the demon king Ravanna.
Diwali also pays tribute to Lakshmi, the goddess of wealth, and lanterns are lit to guide her into people's homes.
Fireworks and festivities are considered an essential part of the celebrations. Credit: Owen Humphreys/PA Wire
What are the Diwali celebrations?
Fireworks and festivities are considered an essential part of the celebrations.
Many lights and oil lamps are lit on the streets and in houses.
Families and friends share sweets, gifts and recite to prayer.
When is Diwali?
The festival is held between October and November, but the date changes every year.
This year Diwali fell on the 30th October.
Watch Jonathan Hill's report here.