To start with, let's quickly clear up the Merck vs. Merck question. Merck KGaA is a German company founded in 1668, making it 358 years old—barely younger than Saint-Gobain at 361 years. As part of its international expansion, Merck KGaA opened a US subsidiary in 1891, Merck & Co. In 1917, the United States nationalized the American subsidiary as part of retaliatory measures against Germany, which it had just entered the war against. The Merck family bought it back at auction in 1919, but both companies have been independent ever since. Merck & Co holds the rights to use the "Merck" name in the United States and Canada, while Merck KGaA owns it in the rest of the world. This hasn't stopped the two laboratories from engaging in chronic legal battles over trademark violations in certain markets, the most recent being in 2016 over the United Kingdom.

The status of the American version of Merck is "Inc.", meaning "incorporated," which is similar to a "société anonyme" (SA). Essentially, it is a company with a legal personality distinct from its owners, who are theoretically not liable beyond their initial investment. Broadly speaking, a joint-stock company is referred to as:
- Inc or Corp (corporation or incorporated) in the United States. Example: Alphabet Inc.
- AG (aktiengesellschaft) in Germany and Switzerland (where some companies use SA instead). Example: Volkswagen AG or Roche Holding AG and Givaudan SA.
- SA (société anonyme) in France, Belgium, Switzerland, Spain, Portugal.... Example: Publicis Groupe SA, Anheuser-Busch Inbev SA, Compagnie Financière Richemont SA, Vidrala, S.A or EDP Renovaveis, S.A.
- SpA (società per azioni) in Italy. Example: ENI SpA.
- NV (Naamloze Vennootschap) in the Netherlands. Example: Adyen N.V.
- PLC (Public Limited Company) in the United Kingdom. Example: Jet2 Plc.
- ASA (allmennaksjeselskap) in Norway. Example: Equinor ASA.
- A/S (aktieselskab) in Denmark. Example: Novo Nordisk A/S.
- AB (aktiebolag) in Sweden. Example: Investor AB.
- Oyj (julkinen osakeyhtiö) in Finland. Example: Nokia Oyj.

We also find limited partnerships, particularly in Germany, where this form is quite common among family-owned businesses. Conversely, this structure is rarer elsewhere, or even completely absent from the universe of listed companies in some countries:
- SCS/SCA (Société en commandite simple or par action) in France. Example: Touax SCA.
- KG or KGaA (Kommanditgesellschaft auf Aktien) in Germany, with two variants. The KG is a simple limited partnership and the KGaA combines the characteristics of a limited partnership with those of a joint-stock company. Example: Merck KGaA.
- SAS/SAPA in Italy. The SAS is a simple limited partnership and the SAPA is a partnership limited by shares.
- SCS/SCA in Spain. The SCS is a simple limited partnership and the SCA is a partnership limited by shares.
- SCS (Sociedade em Comandita Simples) in Portugal.
- LP (Limited Partnership) or SLP (Scottish Limited Partnership) in the United Kingdom.
- LP (Limited Partnership) in the United States. Example: MPLX LP.
- KB (Kommanditbolag) in Sweden.
- KS (Kommandittselskap) in Norway.
- K/S (Kommanditaktieselskab) in Denmark.
- Ky (Kommandiittiyhtiö) in Finland.

Let's also mention the various acronyms for limited liability companies, even if they are not the most common among listed players:
- SARL in France.
- Gmbh (Gesellschaft mit beschränkter Haftung) in Germany and Switzerland. Most Gmbh companies listed in Germany are also KGaAs. Example: DWS Group Gmbh & Co. KGaA.
- SRL in Italy.
- SL in Spain.
- Lda (Sociedade por Quotas) in Portugal.
- BV (Besloten Vennootschap) in the Netherlands. Example: Fastned B.V.
- Ltd in the United Kingdom.
- LLC (Limited Liability Company) in the United States.
- ApS (Anpartsselskab) in Denmark.
- AB (Aktiebolag) in Sweden (the limitation of liability is identical to the Swedish equivalent of an SA).
- AS (Aksjeselskap) in Norway.
- Oy (Osakeyhtiö) in Finland.

Finally, we can also mention some more unique legal forms:
- The SGPS (Sociedade Gestora de Participações Sociais) in Portugal. This is the most common corporate form among the country's listed companies, as it facilitates the holding of other assets. Example: Jeronimo Martins, SGPS.
- The SE (Societas Europaea) in Europe. Example: Scor SE.
- The S Corp (S Corporation) in the United States. A tax-advantaged company where shareholders report gains and losses directly on their personal income tax returns.
- PBC or B Corp (Public Benefit Corporation) in the United States, a for-profit company that includes social responsibility or public interest objectives in its bylaws. Example: Veeva.
- The "Entreprise à mission" in France and "Imprese Sociali" in Italy. These are corporate forms similar to PBCs in the United States.
- The CIC (Community Interest Company) in the United Kingdom. A regulated for-profit company created to serve community interests.
- The Partnership in the United States. In its classic form (General Partnership), partners are jointly and severally liable for the company's debts. However, there are limited liability variants, such as LP (Limited Partnership) or LLP (Limited Liability Partnership).

These lists are not exhaustive and only scratch the surface of the legal implications, but at least you will know what lies behind these sometimes strange acronyms.