Answer: Most of the significant changes to the ACA went into effect on March 23, 2010.
Details: The ACA was signed into law on March 23, 2010, by President Obama. The major or significant changes that went into effect were 1. Grandfathered health plans: This enabled people with existing health plans to keep their plans, provided that the insurer continued to offer the plan. 2. Non-grand fathered health plans: Those who purchased health insurance plans after March 23, 2010, would eventually have to conform to the standards established by the ACA.
Note: Many more changes were scheduled to go into effect after March 23, 2010.