Services Provided

Here begins the difference, but also the huge overlap. These are things that a psychiatrist can do, that a psychologist cannot:

• prescribe medication
• write doctor's certificates
• write doctor's reports, e.g. for other doctors, or for medical insurers.
• confidently send bills to the medical insurance, which will be covered
• enable a psychologist to work under their authority, "delegiert" (see previous post).

People from both professions can do other work besides providing psychotherapy. This post is specifically about psychotherapy.

Psychotherapist
If they do provide psychotherapy, then both psychiatrist and psychologists are very likely, sooner or later, to attend some of the exact same courses. The borders are blurred, and a good psychotherapist can be either a psychologist or a psychiatrist, it matters not (except for the reasonse above).

The differences will lie not in their being a medical doctor, or not, but primarily in their wide range of training, attitude, style, belief, etc..

To qualify as a psychotherapist, they ought to have gone through their own therapy. This means that they will have spend quite some time (at least months, possibly years) during their training in the role of the patient of a senior psychotherapist (who may be a psychistrist or a psychologist).

The purpose (or hope) is that, ideally, by the time a psychotherapist begins treating other patients, they will have dealt with, or at least identified, their own problems, their insecurities, their fears, and so on. This doesn't mean that the psychotherapist is perfect, but it should mean that they have learnt to know themselves, so that they have fixed some of their own pain and some of their own hang-ups, and know their own issues well enough to be able to keep them in check, so that the psychotherapist's own inner difficulties don't get in the way of a patient's therapy.