Foot-and-mouth crisis permitting, the Taoiseach, Mr Ahern, arrives in Cardiff this morning to address the Welsh Assembly.
He will be the first "foreign" leader to do so, and the event will represent another landmark in the new phase of Irish diplomacy which Mr Ahern and key advisers put in place in anticipation of New Labour's commitment to re-draw the constitutional map of the United Kingdom.
The Taoiseach's adviser, Mr Martin Mansergh, and the Irish Ambassador to Britain, Mr Ted Barrington, were heavily influential in securing an Irish first, with the opening of consular offices in Edinburgh and Cardiff. Not only did they anticipate Mr Blair's election and the success of his devolution project; long before the Belfast Agreement became reality, Irish diplomats correctly calculated that any agreement between the Northern Ireland parties would have profound implications for relationships within these islands as a whole.
From the outset the Taoiseach has shown himself enthusiastic about the concept of East/West, as well as North/South, co-operation.
Indeed at the inaugural (and, to date, only) meeting of the British Irish Council in December 1999, it was striking that it was the Taoiseach, and not Mr David Trimble, who felt himself touched by Mr Blair's famous hand of history.
Curiously diffident, the First Minister and Ulster Unionist leader was unsure whether that London event was of particular historic moment or not.
Which certainly surprised close observers, given that unionists had invested such hopes in the new East/West dimension as an essential counter to the North/Southery prioritised by the SDLP and Sinn Fein. And which may in part explain the first public evidence of unrest among unionists here about the evident ongoing success of the Irish diplomatic mission.
In Irish terms, today's event will be celebrated as another building block in cementing the interlinking relationships between the countries and interests embodied in the Good Friday accord.
While Northern Ireland remained a major point of dispute, Dublin necessarily looked to London, with little opportunity or incentive to try to develop the natural economic, political and cultural relationships which might naturally have suggested themselves between Ireland and Wales and Scotland, or for that matter the regions of England.
The abandonment of Articles 2 and 3, the agreement rooted in the principle of consent, and the advent of Scottish and Welsh devolution has changed all that - and the Celtic Tiger, of course, is an important additional factor in the new dynamic.
Yet others see that dynamic in an altogether different light, and may even regard Mr Ahern's presence in Cardiff as further evidence of Dublin's diplomatic mission to secure the break-up of Britain as the necessary precursor to Irish unity.
That certainly is the thesis advanced in an article in the current issue of the Spectator. The writer, Tim Luckhurst, makes two key contentions.
First, that nationalists see the secret to unification "in finessing the relationship with their British neighbours, not in constant argument with Ulster Unionists".
Second, that Irish diplomats think devolved leaders "can be persuaded to regard the relationship between Edinburgh/Cardiff and London as a problem, not an opportunity".
Senior sources say it is simply wrong to see their activities as geared to the achievement of unification - not least because this is no longer the driving purpose of Irish government policy. They point to the agreement and the commitment to "an accommodation the people in Northern Ireland can live with" as "sufficient unto the day and for this generation". And they observe a marked sensitivity to ensure "no purchase is given" to nationalist politicians who might wish to exploit the Irish diplomatic presence in Scotland or Wales for their own separatist purposes.
This assessment, of course, also broadly fits with the pro-agreement Ulster Unionist rationale for doing the deal in the first place. One of Mr Trimble's key allies points to a generational shift, fuelled by sustained economic growth:
"Regardless of whether there is a deep strategy, there is an almost unconscious ethos of Irish representation abroad - `Look at us, we've left the UK and found a bigger, better home.' "
Agreeing that "this doesn't put them [Irish diplomats] in the engine room of the destruction of the United Kingdom", Mr Trimble's ally then accepts the logic implicit in Mr Luckhurst's article: "At the end of the day, of course, they're not meant to value the Union. That's our job, and we still haven't established our presence in Edinburgh or Cardiff."