MMORPG.com Final Fantasy XI COrrespondent Wesley Bond takes a look at the Summoner class in this helpful overview.

Like a Vegas Elvis impersonator, the Summoner is a flashy job that luckily looks better and performs better than most Elvis knockoffs. Summoner is a unique blend of mage and pet class that offers a nice change of pace between solo and party play. In a party, the majority of the time a Summoner will be called upon to be main healer. You will have one of the largest MP pools of any class and the ability to get regenerate it back over time. The reason for your massive MP pool is that your avatars drain your MP while you have them out so it is a must for the job. At higher levels, you may be able to find parties that want you to damage deal and backup heal. The nice thing about playing one is that you can opt to solo if things get stale. You will have to be more careful than a Beastmaster, but it can be done with the proper mob choice. The up side to playing a Summoner is that by itself you don't have to buy a bunch of spells (only for subs) but the downside is you have to defeat the avatars before you can summon them. There are two ways to go about doing this: 1) hook up with high level party and take them down in fights called "Primes" 2) Go one on one with them in a level 20 capped fight called "mini fights". The mini terrestrial fights sounds like the easy route but they are very tough. The mini fights aren't impossible, though your first time in may seem that way, but require the proper planning to win. Best bet is to research these fights posted by other Summoners and work on a strategy for each avatar. You may need to invest in some various potions for MP and health to help things along.

Take A Look at the Summoner