My understanding of "taking refuge" is reciting a mantra. However, is there a certain ceremony to become fully Buddhist? Is it just repeating the mantra X number of times, or is there more to it?
Taking refuge can take many forms. You do not have to recite a mantra, although you may find it a helpful means. Taking refuge is as simple as placing your faith in the Buddha, the Dharma, or the Sangha.
For example, if you are suffering, and you remember the Four Noble Truths, and you settle your concentration on the Noble Eightfold Path -- then you have taken refuge in the Dharma.
Buddhism is a method of practice. If you follow the method, then you are already a Buddhist.
In the Theravada tradition, a person can take refuge in the Buddha by paying homage to the Buddha (Namaskaraya), and reciting the Three Refuges (Tisarana, where “ti” is three and “sarana” means refuge or protection) and undertake to observe the five precepts (Panca Sila). One can recite the following stanza three times by oneself.:
“Namo tassa bhagavato arahato samma sambuddhassa”
What is meant by this Stanza is, “I pay homage to the Blessed One, the Exalted One, the fully Enlightened One” or “I pay homage to the fully Enlightened One who found the truth about the existence and became free of all defilements”. Both interpretations are important for someone starting out, without much knowledge of Dhamma.
But the Buddha himself said that the best way to pay homage to him is to learn Dhamma and to follow the Path. That is the more deeper meaning of the Namaskaraya, “Namo tassa bhagavato arahato samma sambuddhassa”.
I will not elaborate on the Three Refuges (Tisarana) and the five precepts (Panca Sila) as past Ops have already covered this. I would like to share this instead. Once The Buddha said, “Attä hi attano nätho, kö hi näthö paro siyä”, meaning, ”One indeed is one’s own refuge; how can others be a refuge to one?”. Each one has one’s own mind. And that is what is needed to be purified in order to attain a peaceful life now, a better life in the next, or even Nibbana. But it all starts with going for refuge in the Buddha Dhamma & the Sangha.
It is good to recite Namaskaraya, Tisarana, and the precepts, to attain citta pasada or calmness and joy of mind. If one does it with understanding and resolve, it can bring benefits. The five precepts have deep meanings, and thus should not be taken lightly. Even if one does not live upto these 5 precepts, one needs to recite with the intention of doing one’s best to keep the precepts.
That depends mainly on a lineage or on a specific Buddhist teaching you follow, so the definition of 'being a buddhist by practice' varies greatly among different schools, lineages and teachings. Because you have tagged your question as 'mahayana', it would be safer to ask your spiritual master about this topic.
If your question means 'does one become a buddhist by reciting a mantra' than the answer would be 'it depends greatly by your intention and state of mind when you recite it', and also 'what kind of a mantra is in question'. Yet, Buddhism is not Islam and my understanding is that you don't become a buddhist just pronouncing a mantra X times, because motivation and transmission of a mantra matters.
Alan, while it is right that on the path, practicing (Dhamma) is the real refuge to reach the targed of refuge, awakening, which means Buddho, one need those who guide one (Sangha) to be able to make one self an island with the Dhamma (practicing). That means one needs to cut of the greates obstacel fist, and that is wanting to become a "Buddhist". To work against ones usuall desires one works in a way to train one self in what is called practice in veneration or paying respect. This practice goes against the raw defilement. Once a person has gained the throwing away of all what is normaly taken as real (five aggregates) having sacrified them for his refuge, one comes to see the Dhamma, the Buddha as well as the Sangha as it really is. From this time on, one by one self becomes member of the Sangha (in perfect context) and so also knows all the values of the three juweles as they really are. It is foolish and sadly a western or better modern approch to motivate people to see more value in the own person and in becoming "a real Buddhist" so that most never ever start even to work against raw defilement. Thats the maketing of industry to be able to sell a product for many. Usually the training of Veneration as one of the ten meritious deeds, starts with bodily and verbal actions and step by step one also learns how to sacrify the mental factors in the same way. Just such a practice, even if not full comprehended, will be the foundation to be once able to maintain proper attention while hearing the true Dhamma, so able to gain right view and the doing the conductive rites and rites naturally. So one is good introduced to do not wslk the "cool" way, jet still very hot and cut the fundamental practice off right at the beginning. One having become different already would never have a problem with veneration of the gems nor would he/she ever tell somebody that it does not make sense to practice Sila, since veneration of what is worthy to counts as virtue right on the path and staightens one views. A huge topic, leading direct to awakening. Just be taking really refuge in the Gems one becomes a person no more able to fall off the path. Hier a useful short essay:
Refuge: An Introduction to the Buddha, Dhamma, & Sangha, *by Thanissaro Bhikkhu (2001; 74pp./222KB) *PDF
This short book provides an excellent introduction to the most basic principles of Buddhism: the Buddha, Dhamma & Sangha, collectively known as the Triple Gem or Triple Refuge. The material is divided into three parts: (I) an introductory essay on the meaning of refuge and the act of going for refuge; (II) a series of readings drawn from the earliest Buddhist texts illustrating the essential qualities of the Triple Gem; and (III) a set of essays explaining aspects of the Triple Gem that often provoke questions in those who are new to the Buddha's teachings. [book] To request a printed copy of this book, please write to: Metta Forest Monastery, P.O. Box 1409, Valley Center, CA 92082, USA.
Beware of those selling you identity and this or that consciousness like every trader does saying "you can" or "you are worthy" which you would buy, but to what would you seek refuge in in that way?
For more about the pratice (veneration is the ptactice!) see: Respect and veneration - Respekt und Ehrbietung: Apacāyana
It's worthy to note, that this practice is a common in every linieage still folling the Buddha and is not maintained by linieages total outside the lane, those who actualky follow the Nigantas "there is no self, i am nobody and nothing..."
(Note: This is a gift of Dhamma and not meant for commercial use or any other use for wordily gain.)