The first changes came into effect on Monday, 1 April and pages on this site can help people find out which benefits have changed or how else they may be affected.
Other major changes also came into effect from April.
These included Housing benefit for social housing tenants - those in council-owned homes or housing association homes - who have more bedrooms than the new law says they need.
Then there is the Local Council Tax Support Scheme. Council Tax benefit, as it used to be, was abolished at the end of March. It has been replaced by local schemes which have to be administered by councils.
The Local Welfare Assistance Scheme which includes things like crisis loans was also abolished in April and again replaced with local schemes administered by councils.
And the "Benefit Cap" - which limits the total amount of benefits people are able to claim - is being phased in between April and September 2013.