Yama and Niyama are the first two limbs of the eightfold path (_Ashtanga Yoga_) set out in Patanjali's Yoga Sutras. Before posture, breath or meditation, the path begins with ethics: the five Yamas (restraints, how we relate to the world) and the five Niyamas (observances, how we order ourselves). They are the ground on which everything else in yoga is built.
The five Yamas — the restraints
The _Yamas_ are the great vows of non-harm — the disciplines that govern how the yogi acts toward other beings and the world. Patanjali calls them the _mahavrata_, the "great vow," binding regardless of birth, place, time or circumstance.
Ahimsa — non-violence
Ahimsa is non-harming in thought, word and deed toward every living being. It is named first because it is the root of all the other restraints: truth, non-stealing and the rest are simply ahimsa worked out in detail. It is not mere passivity but an active goodwill that refuses to injure even when injury would be easy, and that extends compassion to oneself as well as to others.
Satya — truthfulness
Satya is truth in speech and in the mind behind speech — to see things as they are and to convey them without distortion. The tradition holds satya beneath ahimsa, however: truth must never be made a weapon to wound. The aim is speech that is true, measured, beneficial and kind, so that one's word and one's reality come into alignment.
Asteya — non-stealing
Asteya is abstaining from taking what has not been freely given — not only goods, but credit, time, attention and the fruits that belong to another. At its subtlest it is freedom from the covetous impulse itself, the craving to possess what is not one's own. When the longing to grasp falls away, the tradition says, the practitioner is no longer impoverished by want.
Brahmacharya — continence and right use of energy
Brahmacharya is the disciplined, right use of vital energy — classically continence, and more broadly moderation of the senses so that one's force is not scattered and dissipated. The word literally means "moving in Brahman." For the householder it is read as fidelity and temperance rather than total abstinence; in every case its purpose is to conserve and gather one's energy toward a higher aim.
Aparigraha — non-possessiveness
Aparigraha is non-grasping — taking only what is needed and not hoarding, clinging or accumulating beyond use. It loosens the grip of "mine" on possessions, relationships and outcomes. Freed from the burden of guarding and craving, the mind grows light; Patanjali says one who is firm in aparigraha gains insight into the deeper meaning of life itself.
The five Niyamas — the observances
Where the Yamas turn outward, the _Niyamas_ turn inward — the personal observances by which the yogi orders body, energy and mind. They cultivate the steadiness and clarity that make the deeper limbs of yoga possible.
Saucha — purity
Saucha is cleanliness and purity, both outer and inner — of the body and surroundings, and of the heart cleansed of negative emotion. The outer discipline supports the inner: a clean body and ordered space make a clear, untroubled mind, which the tradition links to cheerfulness, one-pointedness and fitness for self-knowledge.
Santosha — contentment
Santosha is contentment — a settled acceptance of what is, without craving for more or grievance at what is lacking. It is not complacency but an inner sufficiency that frees the mind from the restless pursuit of more. Patanjali holds that from contentment comes unsurpassed happiness, a joy that does not depend on circumstance.
Tapas — disciplined effort
Tapas is heat, austerity, disciplined effort — the willing acceptance of hardship and the steady fire of practice that burns away impurity. It is the determination to keep to one's sadhana through difficulty, comfort and discomfort alike. This inner heat, the tradition says, purifies the body and the senses and brings them under mastery.
Svadhyaya — self-study and study of scripture
Svadhyaya is study — both the reading and recitation of sacred texts and the reflective study of oneself in their light. The two move together: scripture is the mirror, and one's own life is what is examined in it. Through svadhyaya, and especially the repetition of sacred sound (japa), the practitioner draws near to the deeper realities the texts describe.
Ishvara-pranidhana — surrender to God
Ishvara-pranidhana is devotion to and surrender of oneself to Ishvara, the Lord — the offering of all one's actions and their fruits to the divine. It is the bhakti woven through Patanjali's otherwise austere path, the loosening of the ego's grip on results. The Yoga Sutras name it on its own as a direct means to samadhi, the gathered stillness that is yoga's goal.
Ten each — the later expansions
Patanjali gives five Yamas and five Niyamas, but later texts widen the lists to ten each. The _Yajnavalkya Smriti_, the _Shandilya Upanishad_ and the _Hatha Yoga Pradipika_ enumerate ten Yamas — adding such restraints as _kshama_ (forbearance), _dhriti_ (steadfastness), _daya_ (compassion), _arjava_ (uprightness), _mitahara_ (measured diet) and _shaucha_ alongside the original five — and ten Niyamas, including _tapas_, _santosha_, _astikya_ (faith), _dana_ (charity), _hri_ (modesty), _mati_ (right thought), _japa_ and _vrata_. The lists differ slightly from text to text, but all enlarge Patanjali's ethical core rather than replace it.
The first two of the eight limbs
Yama and Niyama are limbs one and two of Patanjali's Ashtanga Yoga — the eight limbs being Yama, Niyama, Asana (posture), Pranayama (breath), Pratyahara (withdrawal of the senses), Dharana (concentration), Dhyana (meditation) and Samadhi (absorption). The ethical foundation is laid first so that everything built on it can hold.