The functional resume or CV (curriculum vitae) concentrates only on your skills and accomplishments, either under one heading or, perhaps, subdivided into, say, Management, Engineering, Commercial etc, dependent upon the individual concerned. 

This type of resume or CV concentrates on what you have done, rather than when or where.
Whilst the functional CV or resume is ideal for ensuring that all relevant experience is demonstrated, and that all possible keywords are utilised, some employers do not like this form of presentation, believing that the applicant is using a functional CV in order to hide a gap or some other defect in their employment history.

Those who should consider a functional CV or resume are:

• Those who are looking for first jobs
• Individuals with diverse career patterns that might be questioned.
• Your career has ’downsized’ a while ago.
• Your age is, perhaps, questionable, and you do not wish to emphasise a long career history. (see CV – Older Workers for detailed discussion)
• Career changers who wish to enter a very different field.
• You have extensive experience from another career path.
• You have changed jobs frequently.
• Those with large gaps in their employment history.
• Persons entering an entirely new field, e.g. Military to civilian.
• Have limited work experience.
• Those looking for a position for which they may be over-qualified.

Advantages

• Takes focus away from gaps and/or inconsistencies in your work record.
• Highlights your accomplishments, your skills, and your experience.
• Is able to consider all past experience, whether career or otherwise.

Disadvantages

• Some employers do not like this approach, believing the writer has something to hide.
• Says nothing about career growth or promotions received.
• Impossible for reader to understand what you did in each job.