Personal is an adjective meaning private or belonging to one individual — "please don't read my personal emails". Personnel is a noun meaning the people employed by an organisation — "only authorised personnel may enter". They also sound different: PER-son-al puts the stress at the front, per-son-NEL at the end.
Different parts of speech entirely
Personal modifies a noun. It marks something as private, individual, or done in person: personal data, a personal favour, personal experience, a personal appearance. It never names a group of people.
Personnel names people — specifically, the workforce of a company, army, hospital or department. It behaves as a collective noun and normally takes a plural verb: "personnel are being redeployed", not "personnel is". It also names the department that manages staff, though most organisations now call that Human Resources.
Each in use
- "She keeps her personal life off social media."
- "This is a personal matter and I'd rather not discuss it here."
- "All medical personnel must complete the training by Friday."
- "The base lost thirty personnel to the reorganisation."
The test
Try substituting staff or employees. If the sentence still works — "all medical staff must complete the training" — you want personnel. If instead you can substitute private or individual, you want personal.
A spelling cue: personnel is the one with the double n, and it is stressed at the end — per-son-NEL. Personal has a single n and the stress at the front — PER-son-al. Say the word aloud and the spelling follows.
The mistakes that show up most
The commonest is a sign or job title reading "Human Resources Personal" or "Personal Department", which turns a staffing office into something oddly intimate. The reverse error — "my personnel opinion" — appears in emails and reads as a typo.
Two further points. Personnel has no plural form: never write personnels. And because it is collective, you cannot say a personnel; the singular is a member of staff or an employee.
As for personal, it does appear as a noun in one narrow sense: the personals, meaning small ads placed by individuals. There is also personable, meaning pleasant and easy to get on with, which is a separate word again and not a synonym for either.
Frequently Asked Questions
Is it "personal file" or "personnel file"?
Both exist and mean different things. A personnel file is the record an employer keeps about an employee. A personal file would be a file belonging to you privately. In an HR context, personnel file is almost always the one meant.
Is personnel singular or plural?
It is a collective noun and normally takes a plural verb: "personnel are required to sign in". There is no plural form "personnels", and you cannot refer to one worker as "a personnel".
Which is used in "authorised personnel only"?
Personnel, with the double n. The sign restricts entry to approved staff, not to private individuals.