There are exactly two ways an occupation qualifies for this permit. You need only one.

Door 1 — a job on the Critical Skills Occupations List

The job must be on the [[CSOL|The Critical Skills Occupations List — the official list of occupations Ireland treats as strategically important and in short supply. Most CSEP applicants qualify through a job on this list]] (Critical Skills Occupations List).
Minimum salary €40,904 per year, and a relevant degree qualification or higher is required.
Recent graduate concession: if you obtained that qualification within the 12 months before you apply, the floor drops to €36,848.

Door 2 — a high salary, almost any job

Any eligible occupation paying over €68,911 per year qualifies — you do not need to be on the CSOL.
The exceptions: jobs on the Ineligible List of Occupations, or any contrary to the public interest.
Without a degree, you must instead have the necessary level of experience.

Two special cases sit alongside these. A nurse or midwife qualifies with a third-level degree or diploma accepted by the [[NMBI|The Nursing and Midwifery Board of Ireland — the regulator whose accepted qualification a nurse or midwife needs to qualify on this route]] for registration. And a public-sector role covered by a public-sector pay agreement uses that agreement's pay rate as the threshold.