Here's a cheat sheet to help you understand the facts and implications of the biggest merger to ever occur in adland.

Proposed name: Publicis Omnicom Group

Top brass: The senior leadership is also rather senior in age. Maurice Levy, 71, and John Wren, 60, will serve as co-CEOs for the first two and a half years of the deal. After that, Mr. Levy will become non-executive chairman and Mr. Wren will continue as CEO. For the first year following closing of the transaction, Bruce Crawford, 84, currently Omnicom chairman, will be non-executive chairman of Publicis Omnicom Group. For the second year following the deal's closing, Mr. Crawford will be succeeded as non-executive chairman by Elisabeth Badinter, 69, currently chairperson of the Publicis Groupe supervisory board. Ms. Badinter, daughter of Publicis Groupe's founder, is Publicis Groupe's biggest shareholder with a 9.1% stake as of year-end 2012 (including her children's holdings). The company's board will have 16 members, consisting of the two co-CEOs and seven non-executive directors from each company.

Headquarters: The company will be headquartered in the Netherlands, with the group's operational offices still led from Paris and New York. The location choice is neutral and offers tax advantages.

Combined revenue as of 2012: $23 billion

Total number of employees: Over 130,000

Joint statement for the deal: "For many years, we have had great respect for one another as well as for the companies we each lead," said Messrs. Levy and Wren. "This respect has grown in the past few months as we have worked to make this combination a reality. We look forward to co-leading the combined company and are excited about what our people can achieve together for our clients and our shareholders."

Efficiency Goals: Aiming for $500 million realized due to operating synergies. That's likely going to require consolidation of real estate, companies and possible headcount elimination, but the execs declined to provide any detail around how those cost-savings will be achieved.

Stock information: Publicis Omnicom Group is expected to be listed on the NYSE and Euronext Paris, traded under the symbol OMC (Omnicom Group's current ticker), and to be included in the S&P 500 and the CAC 40, a French stock-market index. Omnicom shares closed Friday at $65.11, up 81 cents or 1.3%. Shares rose in after-hours trading to $67.15 on merger speculation, approaching their July 18 all-time high ($67.43). Publicis stock closed Friday at 59.35 euros, up 1.5%; shares July 18 reached 60.44 euros, highest since 2000. The companies' combined market cap -- stock-market value -- was $32.5 billion as of Friday ($16.8 billion for Omnicom, the rest for Publicis). The deal was structured so shareholders of Omnicom Group and Publicis Groupe will each end up with about a 50% stake in Publicis Omnicom Group.

Antitrust issues: In the U.S., the two firms' combined revenue was $11.4 billion, twice that of the nearest competitor, WPP. Ad Age DataCenter estimates total 2012 U.S. agency revenue at $35.6 billion based on the sum of estimated revenue of nearly 1,000 agencies analyzed in Agency Report 2013. Omnicom and Publicis in 2012 together accounted for 31.5% of worldwide revenue among the 50 largest agency companies ranked by Ad Age, vs. 22.8% for WPP. The combined company accounted for 41.2% of 2012 revenue among the world's 10 largest media agencies, according to Ad Age estimates. Publicis Omnicom would own three of the world's five largest media agencies, including the four largest U.S. media agencies, according to Ad Age.

Approval process: The companies are hoping the deal will close by year-end 2013 or in the first quarter of 2014. Mr. Levy claims that so far the French government has been supportive of the deal and it will get past regulators, while Mr. Wren says advisers have "not raised any red flags."

Advisers on the deal: Moelis & Co. is financial adviser to Omnicom on the transaction. Rothschild is acting as financial adviser to Publicis Groupe. Legal advisers to Omnicom are Latham & Watkins LLP and De Brauw Blackstone Westbroek. Legal advisers to Publicis Groupe are Wachtell, Lipton, Rosen & Katz; Darrois Villey Maillot Brochier; and NautaDulith N.V. Jones Day provided counsel to Moelis & Co.

Selected major shared clients: Johnson & Johnson, Mars, McDonald's, Pfizer, Procter & Gamble

Potential for conflicts: PepsiCo and Coca-Cola; AT&T, Sprint, T-Mobile and Verizon

Impact on competing players in the ad business: WPP moves to No. 2, well behind the combined Publicis Omnicom. Dwarfed now are Interpublic, Dentsu Inc., Havas and MDC Partners. This deal could set off more acquisition activity as the remaining players look to remain competitive.