Invest NI's chief executive takes the oath and settles into the witness chair.

Alastair Hamilton has provided three witness statement to the inquiry - you'll find them here, external, here, external and here, external.

He's been in his role with Invest NI since 2009 and spent time shortly before that as a DUP adviser at Stormont to the then first minister Ian Paisley.

Image source, RHI Inquiry

Invest NI is an non-departmental public body that was set up to help Northern Ireland's economic development.

Its parent department is Stormont's Department for the Economy - formerly the Department for Enterprise, Trade and Investment (DETI), which ran the RHI scheme.

The inquiry's junior counsel Donal Lunny tells Mr Hamilton that he'll be questioned about whether Invest NI missed an opportunity to tell DETI about some of the flaws in the energy scheme.

BBC News NI

An energy expert working for Northern Ireland's economic development agency identified flaws in the RHI scheme long before the problems were discovered by civil servants at the Stormont department running it.

Alastair Nicol (below) said he consistently flagged up concerns about the initiative with Invest NI.

Image source, RHI Inquiry

He told the inquiry that the scheme had completely skewed the biomass boiler market.

And he said it was "not rocket science" that the lucrative subsidies on offer effectively encouraged claimants to install inefficient heating systems using multiple boilers in order to "grab the RHI money".

BBC News NI

An independent inquiry into the RHI scandal was established in January last year by the then finance minister Máirtín Ó Muilleoir.

He ordered it in the wake of the huge public concern and what was then a developing political crisis surrounding the scheme.

The RHI Inquiry began in November and Sir Patrick Coghlin (below), a retired Court of Appeal judge, is its chair and has been given full control over how it will operate.

Image source, Pacemaker

It will look at:

• the design and introduction of the RHI scheme
• the scheme's initial operation, administration, promotion and supervision
• the introduction of revised subsidies and a usage cap for new scheme claimants in 2015
• the scheme's closure

For more information on the RHI Inquiry, you can read our handy Q&A.

When the scale of the overspend emerged, public and political concern rocketed.

As the minister in charge of the Stormont department that set up the RHI scheme, the Democratic Unionist Party (DUP) leader Arlene Foster faced calls to resign from her role as Northern Ireland's first minister in December 2016.

Image source, Pacemaker

She resisted, and Sinn Féin's Martin McGuinness then quit as deputy first minister in protest at the DUP's handling of what had by then become a full-blown political crisis.

That move brought about the collapse of the Northern Ireland Executive. Now, well beyond a year-and-a-half on from that, Northern Ireland remains without a devolved administration.

You can find much more detail on the RHI scheme in our need-to-know guide.

The budget of the RHI scheme ran out of control because of critical flaws in the way it was set up.

Claimants could effectively earn more money the more fuel they burned because the subsidies on offer for renewable fuels were far greater than the cost of the fuels themselves.

At one point the estimate for the overspend was set at £700m if permanent cost controls weren't introduced - temporary cuts have since pulled the budget back on track for now.

Whatever the scale of the bill, it will have to be picked up by the Northern Ireland taxpayer.

The Renewable Heat Incentive scheme - or RHI for short - came to the fore of the Northern Ireland public's knowledge in late-2016 and the fallout from the scandal attached to it is still being felt in the region's politics today.

Image source, Getty Images

The scheme was set up by the Northern Ireland Executive in 2012 as a way of encouraging businesses to switch from using fossil fuels to renewable sources for generating their heat.

Those who signed up were offered financial incentives to buy new heating systems and the fuel to run them.

It may be a chilly, grey morning up on Stormont hill but the Renewable Heat Incentive Inquiry team always has a spring in its step come Friday.

We'll bring you evidence from two high-level witnesses today - first up is Alastair Hamilton, the head honcho at Northern Ireland's business development agency Invest NI.

And this afternoon we'll hear from Janet McCollum, a former chief executive at the poultry production giant Moy Park, one of Northern Ireland's biggest companies.

The session starts shortly so stay with us for live coverage throughout the day.