Northern Ireland economist
So the Republic of Ireland is finally putting its money where its mouth is with a promise of more than 700m euro to be spent on Northern Ireland's infrastructure.
When politicians spend money they shout it from the rooftops.
Business works in quieter ways and while this investment is big it's nowhere near the scale of that already invested by southern companies in Northern Ireland over the past few years.
The Republic of Ireland is to spend 700m euros on NI's infrastructure.
Whether it's bringing gas to the north west, electricity to Coolkeragh or even a little Baileys Irish Cream direct from its Newtownabbey factory, the southern stake in the northern ranch is a vital part of business life.
Is there a cogent explanation for this investment pattern? Two features stand out.
First, the momentum of investment from south to north has increased in recent years. Second, the range of investments is wide.
The explanation: no business expands its cross-border investment unless it sees a prospect of a profitable return on capital. Why does Northern Ireland seem a better prospect now?
The logic of these decisions can be linked to the wider political and business environment.
Whilst the Troubles were at their worst, investing in Northern Ireland was deterred, plants closed and some investors retreated.
The process has now been reversed.
Business investors have greater confidence that the economy of Northern Ireland is becoming more stable: market prospects and market share are now more influential determinants.
The politicians might not yet make a dramatic claim that they have done the economy a 'power of good'.
However, the behaviour of Irish (and British) investors is a growing vote of confidence that an acceptable level of political stability is in prospect.
Many other businesses have had a longer cross-border connection.
The four main banks are big players both north and south. There are many cross-border issues in the banking business still to be solved.
The existence of two currencies has long been an inconvenience for cross border transactions. The four clearing banks have the unusual privilege that they can profitably print their own sterling bank notes in Northern Ireland.
Investors were previously put off by the Troubles
Bank of Ireland, AIB (including First Trust), and the Ulster Bank all have extensive branch networks on both sides of the border and have an Irish headquarters in Dublin.
The Northern Bank is now Danish-owned and is part of the same group as the National Irish Bank.
Dunnes Stores has operated profitably on both sides of the border for many years.
Musgrave Distribution and Musgrave SuperValu-Centra are subsidiaries of the Cork-based Musgrave Group.
C&C (Cantrell and Cochrane) was originally a Belfast owned firm but is now part of an all-Ireland group, with modern plant producing Magners, in Clonmel.
Old Bushmills is a profitable subsidiary now owned through the Irish part of the Diageo Group.
Glen Electric, now a major international player, started in Northern Ireland in Newry and then Bangor as a spin-off from another firm in Dunleer.
Sangers, the wholesale supplier to the pharmaceutical businesses is now a subsidiary of United Drug, its Dublin-based Irish parent company.
Is the investment flow all one way: south to north? Not all one way, but mainly one way.
Some northern investors have put money in businesses in the south.
Hastings Hotels has a top quality shared investment in Dublin in the Merrion Hotel.
The Quinn Group from Derrylin have expanded their extensive network of investments, north and south, including hotels and insurance.
Viridian is a big player in the electricity generation market in Dublin with new plants at Huntstown.
Several large construction businesses from the north have been winning large contracts across the border, including Grahams (of Dromore), Gilbert Ash and the Lagan Group.
What has all this business investment cost? Estimates are not easy to make.
Baileys Irish Cream now has a factory in Newtownabbey
Including the notional investment by the two Irish-controlled banks, the potential realisable value (which is a very hypothetical concept) must be near to £3.5bn.
Excluding the banks, the other business assets owned by investors from south of the border might well be assessed at over £1.5bn.
Cross-border business is alive, profitable and expanding but don't tell the politicians; they'll only take all the credit!
The following businesses have each recently developed or expanded their business investments in Northern Ireland.
Baileys Irish cream liqueur, in a new factory in Newtownabbey
BGE, in the new natural gas pipeline to the North West
ESB, as a major investor in the new electricity generation plant at Coolkeragh
CRH, as the owners of Northstone (Farrans), the largest local construction firm
Titanic Quarter, where Harcourt Developments leads in urban regeneration
The Quinn Group, expanding output of glass bottles and building materials
Kerry Group (former Golden Vale subsidiaries), with Kerrygold, Dairy Produce Packers (of Coleraine) and the Denny bacon and sausage factory (Craigavon)
Glanbia, making mozzeralla cheese at Mageralin
The Tower Hotel Group, with a new hotel in Derry City
Town of Monaghan Co-op, taking over some dairying from Leckpatrick
Lakeland Dairies, who have purchased Pritchitts in Newtownards
IAWS, whose franchise for Cuisine de France has expanded, and
Independent News and Media, now owning the Belfast Telegraph as well as the Irish Independent
The most recent example of the changing business network was the merger of three medium sized accountancy firms to form the sixth largest all island network: McClure Watters (Belfast) have merged with FGS (Farrell Grant Sparks, Dublin) and Lyons Keenan Kilenade (Longford).
Of course the other "big four", (PwC, KPMG, Deloitte & Touche, Ernst and Young) already have large business offices, north and south.