These two terms get used interchangeably in a lot of sales conversations, which causes real confusion when it’s time to budget for one or write it into a compliance requirement. They’re related, but they answer different questions.
Vulnerability scanning
An automated tool compares your systems against a database of known vulnerabilities and misconfigurations, and produces a list — often long — of potential issues ranked by severity score. It’s fast, repeatable, and good at catching the obvious, known stuff continuously. What it can’t do is tell you whether those findings are actually exploitable in combination, or chain them together the way a real attacker would.
Penetration testing
A person — not a tool alone — actively tries to break in, using scan results as a starting point rather than a final answer. A penetration test chains smaller issues together the way an attacker actually would: a low-severity information leak plus a weak password policy plus an unpatched internal service can add up to full compromise, even if each individual finding looked minor on its own in a scan report.
Which one do you need?
In practice: run vulnerability scans continuously (weekly or monthly) as a baseline, and run a full penetration test at least annually and after any major infrastructure change. Many compliance frameworks explicitly require both, treating them as complementary rather than interchangeable — which they are.