Deloitte is the largest professional services network by revenue and number of employees in the world and is one of the Big Four accounting firms, along with EY, KPMG, and PwC.

[11] There have been a number of controversies surrounding the firm, including Deloitte's involvement in a "potentially misleading" report on illicit tobacco trading in Australia.

[12] The company suffered a major cyberattack in September 2017, causing a breach in client confidentiality and publicizing a significant amount of employee information.

[7] On 1 March 1933, Colonel Arthur Hazelton Carter, President of the New York State Society of Certified Public Accountants and managing partner of Haskins & Sells, testified before the U.S. Senate Committee on Banking and Currency.

[7] In 1972 Robert Trueblood, Chairman of Touche Ross, led the committee responsible for recommending the establishment of the Financial Accounting Standards Board.

[24] In 2009, Deloitte purchased the North American public service practice of BearingPoint (formerly KPMG Consulting) for $350 million after it filed for bankruptcy protection.

[33] In 2016, Deloitte acquired advertising agency Heat of San Francisco, best known for its work Madden NFL from EA Sports and the Hotwire travel website.

[48] According to the company website, Deloitte now refers to the brand under which independent firms throughout the world collaborate to provide audit, consulting, financial advisory, risk management, and tax services to selected clients.

[59] Consulting assists clients by providing services in the offering areas of strategy, analytics and M&A, customer and marketing, core business operations, human capital, and enterprise technology and performance.

[60] In An American Sickness (2017), Dr. Elisabeth Rosenthal attributed to Deloitte a key role in counseling the adoption of "strategic billing" as a way of increasing revenues from hospital business.

She dates this development from 2005, when Deloitte hired Tommy Thompson, former secretary of health and human services, as chairman of its global healthcare practice.

[70] In November 2013, the international development charity ActionAid accused Deloitte of advising large businesses on how they could use Mauritius to avoid potentially hundreds of millions of dollars of tax in some of the poorest countries in Africa.

Deloitte responded by saying that, in the absence of the double-taxation treaties, they advise their clients to avail themselves of arrangements that could result in less taxes being paid to the countries in question.

[83] Deloitte's tax services have been globally recognized by ITR, with the firm notably winning three consecutive best transfer pricing awards in the Americas.

[91] The Securities and Exchange Commission announced on 26 April 2005 that Deloitte had agreed to pay $50 million to settle charges relating to Adelphia's 2000 financial statements.

[98] CPA Ontario has brought disciplinary charges against two Deloitte partners, Felice "Phil" Iorio and Steve Kostich, for professional misconduct related to their work on audits for failed Bondfield Construction.

Bondfield filed for creditor protection in April 2019 and former executives are being sued to recover funds siphoned from the company through a fraudulent invoicing scheme.

[118] In January 2022, South African sugar producer Tongaat Hulett announced that it would be suing Deloitte for failing to detect irregularities in its financial statements from 2011-2018 that led to the equity of the company being overstated by R12 billion.

[120] In September 2003, Deloitte reported to the Canadian Bar Association (CBA) that motor vehicle accident insurance claims for bodily injury had been declining since 1999 adjusted for inflation.

Within hours of release, a member of Deloitte was communicating with Insurance Bureau of Canada without the knowledge of CBA (their client) and providing confidential information.

In a joint statement released by Eskom and Deloitte, the parties agreed that there was no evidence of corruption in the deal, and that there were "technical irregularities" in the procurement process.

[123] In April 2020, Deloitte told AmaBhungane that two directors, Pillay, as well as lead consultant on the Eskom contracts, Shamal Sivasanker, had resigned from the firm effective 31 March 2020.

[128] During 2021, the US Public Company Accounting Oversight Board (PCAOB) fined Deloitte's Canadian affiliate $350,000 as a civil penalty for failure to institute reasonable assurance quality controls.

[131] Auditors asked clients to prepare their own paperwork to show that Deloitte-China had completed audits in at least 21 instances, creating the illusion that it followed relevant requirements when there was no evidence of it doing so.

The Australian Customs and Border Protection Service officials called the report "potentially misleading", and raised concerns about the "reliability and accuracy" of the data.

[134] Public health officials criticised Deloitte's decision to conduct the research, as it added credibility to the tobacco industry's effort to undermine the Australian Government's plain cigarette packaging legislation.

[135][136] Deloitte was awarded a $44 million no-bid contract by the Centers for Disease Control and Prevention (CDC) in the United States to build a website to manage scheduling, inventory, and reporting for COVID-19 vaccination.

[139][140] In September 2017, The Guardian reported that Deloitte suffered a cyberattack that breached the confidentiality of its clients and 244,000 staff, allowing the attackers to access "usernames, passwords, IP addresses, architectural diagrams for businesses and health information".

[148]The select committee chairs (Frank Field and Rachel Reeves) called for a complete overhaul of Britain's corporate governance regime, accusing the big four accounting firms of operating as a "cosy club".

[147] Deloitte Consulting has been heavily involved in building unemployment insurance web portals across various US states, including Ohio, Colorado and Illinois.