Mantra, 
Tantra  and Yantra have since time immemorial been prescribed to awaken    the  self within and as remedial measures to burn off negative karmas. These     are windows to cosmic wisdom and recitation of mantras awakens self-awareness    and internal consciousness which are key to self realisation and divinity. Mantras    like Gayatri, om namah sivay, maha mritunjaya and others are a part of our daily    life. Though we all know some mantra or the other, very few people know and    understand the significance and nuances of it.
What is mantra?
Technically speaking a mantra is a mystical 
formula composed of letters    and words that are meaningful to the initiated. A mantra is a combination of    sacred syllables which forms a nucleus of spiritual energy. The mantra  is also    a collection of “akshara” (syllables) meant to raise the  kundalinin    shakti ( the coiled power that lies dormant in all of us).  This serves as a    
magnet to  attract or a lens to focus spiritual vibrations. According to  upanishads,    ancient scriptures of India, the original abode of the mantra was the primeval    ether. The mantras were directly perceived by the rishis or seers who translated    them into an audible pattern of words, rhythm and melody.
The chanting or reciting of mantras activates and accelerates the creative    spiritual force, promoting harmony in 
all parts of human beings. The repetition    of mantras  over billions of times by countless devotees over the centuries has     brought about a vast reservoir of power which augments the inherent  spiritual    potency of the mantras.
There are at least seventy million mantras in the hindu texts. These are 
classified    as two types :
Pra-siddha Mantra – or those that can be recited by  any person irrespective    of whether they are given by a guru or not  and without a specific objective    of solving a problem.
Kamya-siddha Mantra – which are meant to solve specific problems.
Science of Mantra:
John Woodrof, a retired judge of Madras High Court experienced this. One  proficient    tantrik astonished him by producing fire in wood with the  help of fire mantra    (hreem). Various parts of the body are also  affected by the sounds of the words.    B M Lesario Vasai, an Australian  scientist wrote in one magazine about his own    experience and that of  a sick child. He wrote in detail that by reciting certain    types of  words there was an improvement in their health. It is also well-known     to us that there is an effect produced by the energy created by  reciting mantras    individually or in group; we get a thrill (sensation) in our body whenever we    recite the gayatri mantra in a group, or while praising goddess Durga, even    though we do not understand the significance of these mantras. This is the power    of word energy.
Principal Karmarta of Occult Research College in Pune said in his  discourse    that the letters of the alphabet are not only informal but  they also have close    relation with mantra energy. Each letter of the alphabet according to its pronunciation    makes a specific effect on 
the human  body and mind. He proved this by making    some experiments out of some  letters; he proved that the temperature of the    body increased by 1 
degree  by putting specific stress on the letters in “Ram”,    reciting it 1000  times. It can be proved by all this that the word is not lifeless;     there is life in its energy and rays, this is the science of mantra.
Spoken words get destroyed after making a certain sudden effect. Its energy    gets destroyed, but the energy of mantras remains for a long time. The method    of uttering a mantra is very important. Mantra  has got some rhythm and it has    two types of meaning – word meaning  and word significance. It is not necessary    that every word has some  meaning , but it has its significance and that is a    fact.
Suitability of a mantra:
Who should chant which mantra? The suitability of a mantra should be  judged    before giving it, else the consequences can be negative or  disastrous depending    on the extent of unsuitability. {This is tested  based on the name [names were    based on Janma Rashi (
Moon sign  at birth) and Nama Rashi (sign having the name    letter.)] and the  varna (profession) of the sadhaka and this is done in a few    stages.}  Firstly, the starting letter of the mantra is checked .This is followed    by a check on the total number of letters of the mantra. The third step is to    check the overall impact of all the letters of the mantra. However some mantras    are exempt from this rule. (The list is given below.)
Sex of Mantra:
The mantra can also be classified on the basis of the ending words that have    an impact on the attitude of the practitioner. Masculine mantras  can be identified    by their ending syllable / words like “Vasat” or  “fhut”.    These have the strength to ward off evil and are generally  aggressive. Femininie    mantra (stri) on the other hand is docile and  generally ends with “swaha”    or “vaushat” etc. They require the  practitioner to be dedicated and    make offerings to the deity. Neuter mantra has words like “namah”,    “hum” etc which require the practitioner to submit to the will of    the deity. The choice of a mantra does not depend on the sex of the person.    The choice will depend on the attitude that one wishes to invoke the deity with.
In general, captivation (vasikaran), aversion (ucchatan) and other aggressive    acts are best done with the aid of masculine mantras, while for the destruction    of diseases and general welfare the feminine mantras are preferred. Neuter mantras    can remove black magic and are very protective.
Types of Mantras:
Mantras are used for several purposes, for material gains and for  spiritual    upliftment. The most exalted aim can be spiritual  upliftment, others include    curing of disease, warding off evil,  attaining liberation, gaining wealth, influencing    others, acquiring  powers, and at the lowest and meanest level, harming others.
Shanti karan – (pacification) It is meant for the destruction of  diseases,    general well-being and emancipation from the cycle of  re-birth. These mantras    are for warding off the malefic effects and influence of 
planets and for curing    of diseases.
Vashi karan – (captivation) These mantras, when used in a specific way, are    to bring people under control, and thus one gains one’s desires.
Sthamban – (immobilisation) These mantras deal with all the persons  to stop    acting against you. It is meant for mentally or physically  obstructing a person    or group.
Videshan – (dissension) These mantras are for creating differences  between    people. They are meant for creating differences between  couples or close friends    and allies.
Uchchattan – (aversion) It is meant for making a person hate another person    or place. These mantras deal with the distraction of the mind of enemies, opponents    and other persons so that they stay 
away from  harming you. This can also be    used for persons working against their  country, birthplace, residence, home    and family members.
Maran – (eradication ) It is meant for causing the death of a person (or enemy).    These are death-inflicting mantras through which anybody can be killed.
Warning: These are some of the traditional uses. However, it is a law  of nature    that each and every action has a reaction, so anything  done with a wrong intent    will bounce back on the user. Any evil  intention or act will backfire on the    user only.
Mantra sadhana:
The essential and important parts of the process are:
1. Recitation of the mantra
2. Correct rhythmic pronunciation of the mantra
3. Understanding the meaning of the mantra
4. Reciting the mantra the prescribed number of times
Rules of Mantra:
Mantra should be pronounced properly. If it is not pronounced properly,  its    significance is likely to be changed. This shows that  pronounciation should    be done properly otherwise the meaning gets  changed.
Where the mantra should be broken is important, the meanigng gets changed according    to the place where we break the mantra. That is why we should not pronounce    the mantra if we do not know how to do it. If a mantra is not properly used,    it can have an adverse effect. There is a rhythm for pronouncing the mantra    and the seat is specific, the sitting posture is definite.
The smaller the mantra, the more effective it is. If it is long, it  becomes    difficult to utter and its result is general. If it is small,  it is easy to    utter and its result is very good. The result of  mantra is of three types:
(a) Mantra produces vibrations
(b) Colour is seen because of mantra
(c) Different types of sounds are heard
Some universal mantras which anybody can chant are:
1. Om Namo Narayanaya
2. Om Namah Shivaya
3. Om Tat Sat
4. Gayatri Mantra of Rig Veda
5. Om Namo Bhagavate Vasudevaya
6. Hare Rama Krishna
7. Mahamritunjaya Mantra
Rasi Mantra:
The Janma Rashi is the sign occupied by the moon in the birth chart. Following    are the Rasi mantras :
Aries – Om Vishnave Namah
Taurus – Om Vasudevaya Namah
Gemini – Om Keshavaya Namah
Cancer – Om Radha-Krishnaya Namah
Leo – Om Hariharaya Balamukundaya Namah
Virgo – Om Hrim Pitambaraya Paramatmane Namah
Libra – Om Sri Ram Dasrathaye Namah
Scorpio – Om Narayanaya Namah Om Naraya Namah
Sagittarius – Om Hrim Shrim Krim Dharani Dharaya Namah
Capricorn – Om Shrim Vatsalaya Namaha
Aquarius – Om Shri Upendraya Achyutaya Namah, Om Krim Govinda-Gopalaya Namah
Pisces – Om Krim Rathanga – Chakraya Namah
OM – The cosmic sound Aum, or its condensed form OM,  is the origin of    all other sounds and is itself a mantra. It is  called a pranava or sacred syllable    and symbolises Brahman or the  spiritual reality. The mantra Aum gives birth    to rays of light,  bringing illuminations to the mind. Aum is a one letter mantra,    has  no word meaning but its significance is definite; it is the smallest and     most effective mantra. It is made of 3.5 strokes. These strokes are  linked to    the 3 and a half coils of kunalini (the coiled power that  lies within us). Aum    is so powerful that it is called king of  mantras; some mantras give earthly    happiness, some give emancipation,  some give spiritual happiness, paramarthic    shakti – this mantra of  aum links both earthly life and spiritual life.
Gayatri Mantra:
Lord Krishna in Geeta says that among the mantras he is Gayatri, thus  giving    it a supreme status amongst all the mantras. It is the most  potent and powerful    mantra dedicated to the Sun God. The Sun has been  worshipped as a God across    civilizations – its light, its warmth,  its healing qualities, have inspired    awe and reverence. Without it,  nothing on the earth can thrive or survive and    the gayatri mantra is a  tribute to this power of the Sun. It exerts its influence    over  various levels of existence: physical, mental and emotional. This mantra     has the power to open up the floodgates of the highest intellectual  and creative    capacities. It is a mantra which puts us in touch with  our core, the self and    fills it with light and brightness.
Om bhuh, om bhuvah, om svah, om mahah,
Om janah, om tapah, om satyam.
Tat savitur varenyam bhargo devasya
Dhimahi dhiyo yo nah prachodayat.
Meaning: The word Om is the seven spheres of  existence: earth, water,    fire, air, ether, intelligence and  consciousness. We meditate upon the divine    light of that adorable sun  of spiritual consciousness which stimulates our power    of spiritual  perception.
Note: All those who are interested in choosing a  particular mantra are    requested to consult their guru / astrologer.  Along with the initiation, the    guru can advise on which mantra to  chant, what is the best time, place and position    and how often a  mantra needs to be repeated. Each and every type of mantra has    a  rosary that goes with it.