The main part of ISO 27001, i.e., clauses 4 to 10, have not changed significantly. These clauses include the scope, interested parties, context, Information Security Policy, risk management, resources, training and awareness, communication, document control, monitoring and measurement, internal audit, management review, and corrective actions.
Only the security controls listed in ISO 27001 Annex A have been significantly updated.
In general, the changes are only moderate and were made primarily to simplify the implementation: The number of controls has decreased from 114 to 93, and they are placed in four sections instead of the previous 14. There are 11 new controls, while none of the controls were deleted, and many controls were merged.