(Reuters) – U.S. Health and Human Services Secretary Kathleen Sebelius, President Barack Obama’s top healthcare adviser, apologized on Wednesday over the technology failures that have plagued the rollout of Obama’s healthcare law.

Below is a timeline of events surrounding the launch.

* March 23, 2010 – President Barack Obama signs the Patient Protection and Affordable Care Act into law, with the aim of providing health coverage to millions of uninsured Americans beginning in 2014. It is now widely referred to as Obamacare.

* June 28, 2012 – The U.S. Supreme Court upholds most of the law’s key provisions against legal challenges posed by Republicans and other groups. But the court rules that states can choose whether to expand the Medicaid health insurance program for the poor. Many Republican-governed states opt out.

* November 6, 2012 – Obama is elected to a second term as president, defeating Republican challenger Mitt Romney, who had vowed to throw out the healthcare law.

* December 2012 – Seventeen states and the District of Columbia opt to build and run their own health exchanges, leaving the federal government responsible for building technology to enable insurance enrollment for the remaining 33 states.

* December 13, 2012 – Gary Cohen, the top government official overseeing the exchanges at the Centers for Medicare and Medicaid Services (CMS), tells a House of Representatives health oversight committee that significant progress had been made in developing a federal system for verifying subsidy eligibility under Obamacare and that he was confident exchanges run by the states and the federal government would be ready on October 1.

* March 1, 2013 – The Department of Health and Human Services delays by a year the full-scale rollout of its small business health insurance exchanges.

* March 2013 – Henry Chao, deputy chief information officer at CMS, said at an insurance industry meeting that he was “pretty nervous” about the exchanges being ready by October 1, adding, “let’s just make sure it’s not a Third World experience.” At the same event, his colleague Gary Cohen said, “Everyone recognizes that day one will not be perfect.”

* April 2013 – The Obama administration proposes that large employer-based health plans can impose separate limits on out-of-pocket maximum amounts for a year after businesses said they needed more time to be able to coordinate information from separate providers such as medical and pharmaceutical benefits.

* April 2013 – The administration’s payments to main information technology contractor CGI Federal to build the Healthcare.gov website exceed the contract’s original ceiling of $94 million, as an additional $27.7 million is paid.

* May 2013 – Three more states ask the federal government to take over the technology for their insurance exchanges, leaving the U.S. government responsible for 36 state exchanges.

* May 2013 – Obama says the government is working hard to meet its deadlines on the rollout but signals the possibility of problems: “Even if we do everything perfectly, there’ll still be, you know, glitches and bumps,” he said.

* June 19, 2013 – The Government Accountability Office says the health insurance exchanges may not open on time because they have missed deadlines and are behind schedule, including on testing the system.

* July 2, 2013 – The Obama administration delays by a year a key component of the law requiring employers to provide health insurance for their workers or pay a fine to the Internal Revenue Service for each full-time employee.

* July 2013 – British outsourcing group Serco wins a contract to handle paper applications for exchange-based health plans. The deal is worth up to $1.25 billion including four optional one-year extensions. Separately, the company is investigated by Britain’s Serious Fraud Office for questions about its billing.

* July 7, 2013 – HHS delays until 2015 requirements that exchanges verify income and allows random rather than comprehensive checks on employer-based insurance status for 2014.

* July 31, 2013 – Marilyn Tavenner, the top CMS officials, testifies that final “dress rehearsal” testing for the data hub was underway and would continue until just before October 1.

* August 6, 2013 – The HHS inspector general says in a report that the federal government is months behind in testing data security for the exchanges.

* August 9, 2013 – Oregon says it will not allow wide public access to its Obamacare exchange for the first few weeks of October, and consumers can sign up with the help of trained advisers.

* August 28, 2013 – The Obama administration delays the signing of final agreements with insurance plans. Insurers complain about technical glitches disrupting the display of the new insurance plans, including medical charges and deductibles, in testing.

* August 2013 – The administration pays CGI an additional $58 million for Healthcare.gov.

* September 10, 2013 – Obamacare is likely to have a “rocky” enrollment start on October 1 in some U.S. states because of ongoing technology challenges facing new online health insurance exchanges, W. Brett Graham of the Salt Lake City-based consulting firm Leavitt Partners says in testimony to a House of Representatives panel. At the same hearing, contractor CGI says it was on schedule to launch the federal exchange.

* September 2013 – Colorado and the District of Columbia say that not all of their websites’ functions will be ready on October 1 when their exchanges start running.

* September 2013 – The government spends another $18.2 million with CGI.

* September 26, 2013 – The Obama administration says that federal sites to offer health insurance to small businesses and to Spanish-speaking consumers are delayed.

* October 1, 2013 – Technology problems and heavy internet traffic stall the launch of the new online insurance exchanges, with the federal Healthcare.gov site inaccessible to millions of Americans. An administration official says the problems would be resolved within hours. President Barack Obama compares the website’s issues to the glitchy rollout of the latest Apple operating system. On the same day, a Republican-led effort to defund Obamacare holds up national budget provisions, triggering a federal government shutdown.

* October 17, 2013 – Failing to wrest any major concessions from the Obama administration, Republican lawmakers agree to budget provisions that allow the federal government to re-open.

* October 22, 2013 – With Healthcare.gov’s technology problems continuing into a third week, President Obama names trusted adviser Jeffrey Zients to run a “tech surge” of experts to fix the website.

* October 24, 2013 – Republican opposition to the law turns to exposing the failed launch of Healthcare.gov, beginning with a hearing of the House Energy and Commerce Committee focused on CGI and other government IT contractors. They testify that they had only two weeks to test the new system behind Obamacare, compared with weeks, or months, as would be expected for such a large project.

* October 24, 2013 – The Obama administration says about 700,000 Americans have filed applications to determine their eligibility for government assistance under Obamacare across the country. Data on how many people have actually enrolled in coverage is expected in mid-November.

* October 25, 2013 – White House adviser Zients declares the federal Healthcare.gov website “fixable” and says it would be operating smoothly by the end of November.

* October 27 – An outage at the data center hosting federal data stops enrollment across the country and brings down Healthcare.gov for a day.

* October 30 – HHS chief Sebelius apologizes for the botched launch, calling it a “debacle,” and says that she should be held responsible for the problems.

(Reporting by David Morgan and Caroline Humer; Editing by Will Dunham)