The Bank of Ireland (Irish: Banc na hÉireann) is a commercial bank operation in Ireland and one of the traditional 'Big Four' Irish banks.

Historically the premier banking organisation in Ireland, the Bank occupies a unique position in Irish banking history. At the core of the modern-day group is the old Bank of Ireland, the ancient institution established by Royal Charter in 1783.

Bank of Ireland is the oldest bank in continuous operation (apart from 4 closures due to bank strikes, 1950, 1966, 1970, 1976) in Ireland.

The history is as follows:

The Bank of Ireland is not, and was never, the Irish central bank. However, as well as being a commercial bank – a deposit-taker and a credit institution – it performed many central bank functions, much like the earlier-established Bank of Scotland and Bank of England. The Bank of Ireland operated the Exchequer Account and during the nineteenth century acted as something of a banker of last resort. Even the titles of the chairman of the board of directors (the Governor) and the title of the board itself (the Court of Directors) suggest a central bank status. From the foundation of the Irish Free State in 1922 until 31 December 1971, the Bank of Ireland was the banker of the Irish Government.

The headquarters of the bank until the 1970s was the impressive Parliament House on College Green, Dublin. This building was originally designed by Sir Edward Lovett Pearce in 1729 to host the Irish Parliament, and it was the world's first purpose-built bicameral parliament building.

The bank had planned to commission a building designed by Sir John Soane to be constructed on the site bounded by Westmoreland Street, Fleet Street, College Street and D'Olier Street (now occupied by the Westin Hotel). However, the project was cancelled following the Act of Union in 1800, when the newly defunct Parliament House was bought by the Bank of Ireland in 1803. The former Parliament House continues today as a working branch. Today, visitors can still view the impressive Irish House of Lords chamber within the old headquarters building. The Oireachtas, the modern parliament of the Republic of Ireland, is now housed in Leinster House in Dublin. In 2011, the Irish Government set out proposals to acquire the building as a venue for the state to use as a cultural venue.

In the 1970s the bank moved its headquarters to a modern building on Lower Baggot Street, Dublin 2. As Frank McDonald notes in his book Destruction of Dublin, when these headquarters were built, it caused the world price of copper to rise – such was the usage in the building.

In 2010 the bank moved to a new, smaller headquarters on Mespil Road.

The Group provides a broad range of financial services in Ireland to the personal, commercial, industrial and agricultural sectors. These include checking and deposit services, overdrafts, term loans, mortgages, international asset financing, leasing, instalment credit, debt financing, foreign exchange facilities, interest and exchange rate hedging instruments, executor and trustee services.

The bank is headquartered in Dublin, and has operations throughout the Republic of Ireland. It also operates in Northern Ireland, where it prints its own banknotes in Pounds Sterling (see section on banknotes below). In Great Britain, the bank expanded largely through the takeover of the Bristol and West Building Society in 1996. Bank of Ireland also provides financial services for the British Post Office throughout the UK. Operations in the rest of the world are primarily undertaken by Bank of Ireland Corporate Banking who provide services in France, Germany, Australia and the United States.

Although the Bank of Ireland is not a central bank, it does have Sterling note-issuing rights in the United Kingdom. While the Bank has its headquarters in Dublin, it also has operations in Northern Ireland, where it retains the legal right (dating from before the partition of Ireland) to print its own banknotes. These are pound sterling notes and equal in value to Bank of England notes, and should not be confused with banknotes of the former Irish pound.

The obverse side of Bank of Ireland banknotes features the Bank of Ireland logo, below which is a line of heraldic shields each representing one of the six counties of Northern Ireland. Below this is a depiction of a seated Hibernia figure, surrounded by the Latin motto of the Bank, Bona Fides Reipublicae Stabilitas ("Good Faith is the Cornerstone of the State"). The current series of £5, £10 and £20 notes, issued in April 2008, all feature an illustration of the Old Bushmills Distillery on the reverse side. Prior to 2008, all Bank of Ireland notes featured an image of the Queen's University of Belfast on the reverse side.

The principal difference between the denominations is their colour and size:

The Bank of Ireland does not issue banknotes in the Republic of Ireland. Section 60 of the Currency Act 1927 removed the right of Irish banks to issue banknotes, however "consolidated banknotes", of a common design issued by all "Shareholder Banks" under the Act, were issued between 1929 and 1953. These notes were not legal tender.

Michael Soden abruptly quit as group chief executive on 29 May 2004 when it was discovered that adult material that contravened company policy was found on his Bank PC. Soden issued a personal statement explaining that the high standards of integrity and behaviour in an environment of accountability, transparency and openness, which he espoused, would cause embarrassment to the Bank.

An IR£30.5 million tax arrears liability was settled by Bank of Ireland in July 2000. The Bank told the Oireachtas Public Accounts Committee Inquiry that its liability was in the region of £1.5 million. The settlement figure was 'dictated' by the Revenue Commissioners following an audit by the Commissioners. It was in Bank of Ireland that some of the most celebrated of the "celebrated cases" of non-compliance and bogus non-resident accounts have to date been discovered and disclosed. Thurles, Boyle, Roscrea (1990), Milltown Malbay (1991), Dundalk (1989/90), Killester (1992), Tullamore (1993), Mullingar (1996), Castlecomer, Clonmel, Ballybricken, Ballinasloe, Skibbereen (1988), Dungarvan and, disclosed to the Oireachtas Public Accounts Sub-Committee, Ballaghaderreen (1998) and Ballygar (1999). The Public Accounts Sub-Committee Inquiry concluded that "the most senior executives in the Bank of Ireland did seek to set an ethical tone for the bank and unsuccessfully sought Revenue Commissioners assistance to promote an industry-wide Code of Practice.

In April 2008 it was announced that four laptops with data pertaining to 10,000 customers were stolen between June and October 2007. This customer information included names, addresses, bank details, medical and pension details.

The thefts were initially reported to the Garda Síochána, however the Banks senior management did not know about the problem until February 2008 after an internal audit uncovered the theft and the Bank did not advise the Data Protection Commissioner and the Central Bank of Ireland until mid-April 2008. It also came to light that none of the laptops used encryption to protect the sensitive data. The Bank has since released a press release detailing the seven branches affected and its initial response, later in the month the Bank confirmed that 31,500 customer records were affected as well as an increased number of branches.

On 27 February 2009 it was reported that a criminal gang from Dublin had robbed €7 million from the Bank of Ireland's main branch in College Green. The robbery was the biggest in the history of the Republic of Ireland, during which a girlfriend of an employee, her mother and her mother's five-year-old granddaughter were held hostage at gunpoint. Gardaí arrested six men the next day, and recovered €1.8 million. A spokesperson for the bank said: "Bank of Ireland's priority is for the safety and well-being of the staff member and the family involved in this incident and all of the bank's support services have been made available to them."

The information provided to the Department of Finance in 2009 in advance of a recapitalisation of the bank which cost the taxpayer €3.5 billion "was incomplete and misleading". It also gave wrong information to the Minister for Finance who in turn misled the Dáil on €66 million in bonuses it paid since receiving a State guarantee. External examiners found it used "a restrictive and uncommon interpretation of what constituted a performance bonus". Their report also found that there had been "a catalogue of errors" and that the information supplied by Bank of Ireland to the Department of Finance was "presented in a manner which minimised the level of additional payments made". The Bank paid €2 million by way of compensation to the Exchequer for providing "misleading" information.

The Bank has forged strong links with IT outsourcing companies since 2004 or earlier. On 1 November 2010 IBM won the $450M full scope outsource contract to manage BoI Group's Information Technology (IT) infrastructure services (e.g. mainframe, servers, desktops and print services) in a competitive bid against HP (the incumbent outsource provider) and HCL. This follows on from the Bank's natural expiration of its current agreement with HP, which was signed in 2004.

Following a competitive bid process with a number of parties, IBM was selected for exclusive contract negotiations in July 2011. During the intervening period, an extensive due diligence phase has been undertaken and relevant regulatory approval has been granted. IBM will manage the Group's entire IT infrastructure, including desktop systems, servers, mainframes, local area networks and service desk. Since then, BOI has given HCL a €30m Business Process Outsourcing contract and has selected them as strategic local resourcing partner in Ireland. In addition to that, HCL have opened a software factory for Bank of Ireland in India and has started to outsource production support for the retail banking and payments applications in BOI. This exclusive relationship with HCL has been seen as controversial in the context of the substantial Irish taxpayer investment in Bank of Ireland – and the lack of any significant investment by HCL in Ireland. A banking analyst said in July 2011 that BOI's IT system is "very antiquated."

Bank of Ireland closed the accounts of Irish Palestine Solidarity campaign citing that the bank considered Palestine a high risk country. Sinn Féin TD Mary-Lou McDonald called this outrageous and an insult to the Palestinian people.

On 5 March 2009, the shares reached €0.12 during the day, thereby reducing the value of the company by over 99% from its 2007 high. At the 2009 AGM, shareholders criticised the performance of their Auditors, PriceWaterhouseCoopers.

The Central Bank told the Oireachtas Enterprise Committee that shareholders who lost their money in the banking collapse are to blame for their fate and got what was coming to them for not keeping bank chiefs in check, but did admit that the Central Bank had failed to give sufficient warning about reckless lending to property developers.