Yoga is defined as a systematic methodized effort to balance and directs various levels of one's own energy, for self-perfection or for a union of the human individual with the universal transcendent Existence. This does not refer only to the physical body, but the entire being, including the intellectual and emotional processes. There are four primary paths to yoga. They are:

Path of Devotion (Bhakti-yoga):
The path of devotion aims at the enjoyment of the supreme Love and Bliss. It focuses on realization of Truth (true reality, true potential) through means of devotion and surrender. Prayers, rituals, and ceremonial processes are its basic approach. Chanting, singing, and repeating God's name are also important practices. In the initial stage of spiritual progress, a temple or similar place is needed to practice Bhakti yoga. Ultimately, Bhakti yoga develops humility within and dissolves ego or I ness. This is an excellent form of yoga for emotionally oriented people.

Path of Knowledge (Jnan-yoga): 
The path of knowledge aims at the realization of the unique and supreme SELF. Intellectually oriented people prefer this path because it uses study, thinking, direct inquiry, and contemplation as its practices. This path is typified by spiritual discrimination between what is real (true reality) and what is unreal or illusion (Maya) in the universe.

The path uses the intellect as a means to negate bondage to the material world through inquiry and analysis. The mind itself is used to examine its own nature. This is typified by inquiring of oneself through meditation "Why am I here?" "What is real and unreal?" and the biggest question of all "Who am I?" This leads to the ultimate realization of truth. In the initial stage, one requires the guidance of a true teacher or scriptures to practice Jnana yoga.

Path of Action (Karma yoga):
The path of action aims at the dedication of every human activity to the supreme Will. It is the yoga of action and selfless service for the benefit of humanity at large. This includes social work, ecology, environmental protection, education, animal protection and the like. It can be practiced anywhere at any time. Ultimately the person dedicates all Works and Services as an offering to God, without any expectation of results or personal gain. This dissolves one's ego or I ness. This is an excellent form of yoga for action oriented people.

Path of Self Control and Meditation (Raja-yoga or Astang-yoga):
Raja yoga aims at the liberation and perfection not only of the body, but also of the mental being, the control of the emotional and sensational life, the mastery of the whole apparatus of thought and consciousness. It is the science of physical and mental control. A great sage, Shri Patanjali, pioneered it. It is also known as Astanga yoga, or the yoga of eight steps.

All eight steps are important and are to be followed sequentially, leading to the ultimate realization of Truth or God. 

1) Yama restraints
In the initial stage, a person should restraint from violence, untruthfulness, non chastity, stealing, and material possessions.

2) Niyama observances
In the second stage, a person should develop virtues like cleanliness (external and internal), contentment, austerity, religious study, and self surrender to God.
The first two stages are meant for moral purification, without these no spiritual progress is possible.

3) Asana physical exercise
In the third stage, a person should do physical exercise (Hatha yoga) to keep the body healthy and the spinal cord straight in preparation for long periods of meditation (1 hour).

4) Pranayama rhythmic breathing 
In the fourth stage, a person should practice regularly the control of vital energy through certain breathing techniques. Rhythmic breathing helps concentration of the mind. 
Sitting still (step 3) and rhythmic breathing (step 4) makes the mind fit for looking inward.

5) Pratyahara detachment of mind
In the fifth stage, a person should practice detachment or divorcing of mind from the five senses (touch, taste, smell, sight, and sound) which provide pleasant or unpleasant feelings. This mental exercise gradually slows the rush of thoughts from within to the surface of the mind. Now the mind has become ready for concentration on one object or on one idea.

6) Dharana removal of thoughts
In the sixth stage, a person should concentrate the mind either on one external object or one internal idea upon which to meditate. One finds that, in spite of the best of efforts, the mind does not remain glued to the chosen object. The object appears too hazy and there are breaks in concentration. One has to make repeated attempts during Dharana which ultimately lead to emptying all other thoughts.

7) Dhyana meditation
The thought removal process (Dharana) leads naturally to meditation (Dhyana) in the seventh stage. Meditation is an unbroken flow of thought towards an external object or an internal idea. 

8) Samadhi super conscious state Through intense practice, meditation turns into Samadhi. In Samadhi a person is unconscious of everything about oneself. Even the object of meditation melts away but the vision of the object occupies the entire mind. The knowledge of the object becomes complete.

The goal is to arrive at the liberating Truth, Beatitude and Infinity, which is the nature of the spiritual life. Love, Knowledge, and Action are the three divine powers in human nature. The path of knowledge (Jnana-yoga) is the primary path of liberation for Jainism and Buddhism. However, many components of Raja-yoga such as Yama and Niyama are accepted in this path during the earlier stage of the spiritual progress. Different sects of Hinduism cover all different paths of yoga and their combinations. Christianity, Islam, Judaism, and Sikhism follow the path of surrender or devotion (Bhakti-yoga).

A person does not need to be searching for God to practice yoga. One only needs to have a desire to free oneself from the bonds that restrict oneself from being truly free. Once these bonds are broken, one realizes the true human potential, the true reality, and the God within. A person can attain the total freedom or realize God within using any of the four paths. However at the final liberating state, all paths merge, meaning the ultimate spiritual quality and characteristics of all liberated persons (souls) are same. In this technological age of economic and scientific achievements, it is quite remarkable to see that these yoga practices, which are thousands of years old, are still the proper and effective paths to the realization of the ultimate reality.