The "in care of" notation tells the postal service and the initial recipient to forward your letter to the intended reader. It appears more often than people think: forwarding correspondence to a consultant working at a client's office, reaching a public figure through their management, or sending documents to a guest staying at a hotel. Get the format wrong and your letter stalls at the wrong desk.
What "in care of" actually means
The notation means your letter is physically delivered to one party (the intermediary) with the expectation that they pass it on to the actual addressee. The intermediary doesn't own the correspondence. They simply hold the address where delivery is possible.
The abbreviation is c/o. Write it in lowercase with a forward slash and no spaces. Some older style guides permit "C/O" in full caps, but c/o is the current standard in most professional contexts. Never write "care of" spelled out across the address block itself; the abbreviation is both correct and cleaner.
Where to place the notation in the address block
The c/o line sits on the line immediately below the recipient's name and immediately above the street address. This placement is specific. Moving it elsewhere breaks the postal logic the address block is built on.
A correctly formatted address block looks like this:
Ms. Elena Vasquez
c/o Horizon Consulting Group
44 Pemberton Street, Suite 300
Boston, MA 02108
The street address and city belong to the intermediary, not to Ms. Vasquez. That's the point: the postal service needs a physical address to deliver the letter, and the intermediary provides it.
If you're working within proper business letter format, the inside address is where the full c/o block appears. The salutation still addresses the intended recipient by name, not the intermediary.
How the inside address and c/o line interact
Writers sometimes wonder whether to include the intermediary's name separately, or whether the c/o line replaces it. The c/o line includes the intermediary's name. You don't write it twice.
Compare these two versions:
Incorrect:
Horizon Consulting Group
Ms. Elena Vasquez
c/o Horizon Consulting Group
44 Pemberton Street, Suite 300
Correct:
Ms. Elena Vasquez
c/o Horizon Consulting Group
44 Pemberton Street, Suite 300
Boston, MA 02108
If the intermediary is a person rather than an organisation, the same logic applies. The recipient's name comes first, then c/o followed by the individual holding the address.
For more on how each component of the inside address fits together, see our guide on how to write a business letter inside address, which covers name order, title formatting, and multi-line address rules.
When you actually need the c/o notation
Three situations call for it most often in professional correspondence:
- The recipient works temporarily at a third party's location (a contractor, visiting consultant, or seconded employee).
- The recipient receives mail through a representative, such as an agent, attorney, or manager.
- You're sending a document to a person at an institution or organisation that holds their address on your behalf.
What the notation doesn't cover: delivering to a shared office where no forwarding is expected, or addressing a department within a company. Those situations use a department line or an attention line instead.
Common mistakes to avoid
The most common error is inverting the name order: placing the intermediary first and the recipient second. This confuses both the postal service and the intermediary's mail room. The letter is for the recipient. Their name leads.
A second mistake is writing out "care of" in full inside the address block. Save the full phrase for conversational references ("send it care of their London office"). In the address block itself, c/o is the correct form.
Third: don't omit the notation when it's needed and hope the intermediary figures it out. A letter arriving at an organisation with no routing instruction can sit undelivered for days. The c/o line is what gives the intermediary permission and instruction to forward.
The salutation still addresses the recipient
Once the envelope is addressed correctly, the letter itself proceeds as normal. Open with the salutation directed at the person you're writing to, not the intermediary. If you're writing to Ms. Vasquez, open with "Dear Ms. Vasquez:" regardless of whose office physically receives the letter.
The intermediary's role ends at the mailroom. Inside the letter, your correspondence is between you and the intended reader. Keep those two relationships separate and your letter will read cleanly at every stage of its journey.