Alex Salmond's visit to Stormont is not the first time a Scottish First Minister has addressed Northern Ireland Assembly members.
By Mark Devenport
BBC NI Political Editor
But it represents a new start to what promises to be a fascinating relationship between the United Kingdom's two northern devolved governments.
When Jack McConnell made his speech in the Stormont senate chamber in May last year, he added his weight to a concerted campaign by the Labour government to persuade the Northern Ireland parties to restore devolution.
Alex Salmond will address the NI Assembly
He didn't put a foot wrong, but his pro-devolution argument was part of a backdrop to the efforts of British and Irish prime ministers Tony Blair and Bertie Ahern and Northern Ireland Secretary Peter Hain.
Now Stormont is up and running and the SNP has formed a minority government in Edinburgh, the equation is different.
First of all, no-one should presume that because Mr Salmond is a nationalist and Mr Paisley is a unionist that the two men are political opponents.
The DUP leader congratulated the SNP leader on his election success and pointed out that Mr Salmond's nationalism doesn't rule out keeping the Queen as a head of state.
The two parties have long enjoyed a close relationship in the corridors at Westminster. Moreover, for many in the DUP, Ulster Scots fellow feeling transcends political labels.
Beyond such sentiments, there is a recognition that the two near neighbours across the North Channel must strive to cooperate.
On a practical level, unionists want improved roads and other links between Scotland and Northern Ireland.
The two northern executives will always want more cash, more power and more ability to respond flexibly to local conditions. And those common interests could bring them into conflict with Westminster.
Around the time of the Scottish parliamentary elections, politicians in Edinburgh were closely watching the efforts of the Northern Ireland parties to persuade Gordon Brown to approve a regional cut in the rate of corporation tax.
Scotland argued that if Northern Ireland achieved such a cut, it should follow suit. Northern Ireland responded that it was in a unique position because of competition for investment from the Irish Republic with its low tax rate of 12.5%.
But since then, the Northern Ireland parties have been disappointed by what they view as the lack of generosity from the chancellor over a "peace dividend".
There is little optimism that the former head of the Inland Revenue, Sir David Varney, will recommend a regional reduction in corporation tax after reviewing the matter.
If they feel let down by the future Scottish resident of Downing Street, the Northern Ireland parties may conclude there is nothing to be lost by working closely together with Gordon Brown's bete noir, Mr Salmond.
Could this prove a headache for Gordon Brown?
The SNP leader has called for a plenary body to represent the devolved nations vis-a-vis Westminster.
The pre-existing British Irish Council, which covers east-west relations across the British Isles has, until now, been a marginal institution, but it could become more relevant.
Things could get even more interesting if the next general election produces a hung parliament in which both Northern Ireland unionist votes and Scottish nationalist votes carry more clout.
There is, however, a danger from the unionist perspective.
The English are already becoming increasingly restive about the level of subsidy going towards their northern cousins and the anomalies which devolution has caused at Westminster, where Scottish and Northern Ireland MPs can vote on English matters, but not vice versa.
A vibrant axis between Belfast and Edinburgh makes all kinds of sense in the short to medium term.
But whilst Scottish and Irish nationalists may be perfectly happy to see an ever widening divide with the "Sassenachs", Northern Ireland unionists who value their place in the UK, may ponder whether they want to wake the sleeping giant of English nationalism.
Watch live stream of Scottish First Minister's Stormont address here from 1600