Both adults in a stable relationship are now able to become the legal parents of an adopted child.
Before the revision to the adoption law, only married or single people could become adoptive parents, with only one of the adults in unmarried couples able to be legally recognised as parent.
"These changes will have a major impact on thousands of families," said Felicity Collier, chief executive of the British Association for Adoption and Fostering.
"Opening up adoption to unmarried partners will encourage more people to consider adoption and this is very important at a time when too many children wait too long in temporary care waiting for an adoptive family."Birth mothers and other birth relatives also have the right to trace children they put up for adoption once they become adults under the Adoption and Children Act 2002.
The birth mothers and relatives now have the legal right to ask for an intermediary service to find the child and ask if they would like to be contacted.
"We believe there are many adopted adults who have not made the first approach in case it is not welcomed by their birth parent but who would want to respond if they knew their birth parent was concerned to know how they were," Collier said.
The new law also gives foster carers and relatives the right to apply for special guardianship orders which are expected to last until the child is 18. The special guardianship will hand all responsibility for the child over to them instead of the local authority.
