Yoga Sūtras
The Yoga Sūtras of Patañjali form the basis of the modern practice of yoga. It is guide to yoga, consisting of short aphorisms. Yoga itself is described as follows:
योगश्चित्तवृत्तिनिरोधः ॥२॥
yogaś citta-vritti-nirodhaḥ ॥ 2 ॥
Yoga is the stilling of the changing states of the mind.
— Yoga Sūtras of Patañjali, 1.2.[1]
Patañjali describes a comprehensive yoga practice consisting of eight limbs: aṣṭāṅga yoga.
The eight limbs of aṣṭāṅga yoga
यमनियमासनप्राणायामप्रत्याहारधारणाध्यानसमाधयो ऽष्टाव अङ्गानि ॥२९॥
yama-niyamāsana-prāṇāyāma-pratyāhāra-dhāraṇā-dhyāna-samādhayo 'ṣṭāv aṅgāni ॥ 29 ॥
The eight limbs are yama, niyama, āsana, prāṇāyāma, pratyāhāra, dhāraṇā, dhyāna, samādhi.
— Yoga Sūtras of Patañjali, 2.29.[1]
These eight limbs are then explained one by one. More information about each of the eight limbs can be found on the separate pages on them (follow the links).
Yamas
अहिंसासत्यास्तेयब्रह्मचर्यापरिग्रहा यमाः ॥३०॥
ahiṁsā-satyāsteya-brahmacaryāparigrahā yamāḥ ॥ 30 ॥
The yamas are ahiṁsā (nonviolence), satya (truthfulness), asteya (refrainment from stealing), brahmacarya (moderation), aparigraha (renunciation of unnecessary possessions).
— Yoga Sūtras of Patañjali, 2.30.[1]
Niyamas
शौचसन्तोषतपःस्वाध्यायेश्वरप्रणिधानानि नियमाः ॥३२॥
śauca-santoṣa-tapaḥ-svādhyāyeśvara-praṇidhānāni niyamāḥ ॥ 32 ॥
The niyamas are śauca (cleanliness), santoṣa (contentment), tapas (discipline), svādhyāya (self-study), īśvara-praṇidhānāni (surrender to something larger than yourself).
— Yoga Sūtras of Patañjali, 2.32.[1]
Āsana
स्थिरसुखमासनम् ॥४६॥
sthira-sukham āsanam ॥ 46 ॥
The āsana (posture) should be steady and comfortable.
— Yoga Sūtras of Patañjali, 2.46.[1]
Prāṇāyāma
बह्याभ्यन्तरस्तम्भवृत्तिः देशकालसङ्ख्याभिः परिदृष्टो दीर्घसूक्ष्मः ॥५०॥
bāhyābhyantara-stambha-vṛttiḥ deśa-kāla-saṅkhyābhiḥ paridṛṣṭo dīrgha-sūkṣmaḥ ॥ 50 ॥
Prāṇāyāma (breath control) manifests as external, internal and restrained movements of breath. These are drawn out and subtle in accordance to place, time and number.
— Yoga Sūtras of Patañjali, 2.50.[1]
Pratyāhāra
स्वविषयासम्प्रयोगे चित्तस्य स्वरूपानुकार इवेन्द्रियाणां प्रत्याहारः ॥५४॥
svaviṣayāsamprayoge cittasya svarūpānukāra ivendriyāṇāṁ pratyāhāraḥ ॥ 54 ॥
Pratyāhāra, withdrawal from sense objects, occurs when the senses do not come into contact with their respective sense objects. It corresponds, as it were, to the nature of the mind (when it is withdrawn from the sense objects).
— Yoga Sūtras of Patañjali, 2.54.[1]
Dhāraṇā
देशबन्धश्चित्तस्य धारणा ॥१॥
deśabandhaścittasya dhāraṇā ॥ 3 ॥
Dhāraṇā (concentration) is the fixing of the mind in once place.
— Yoga Sūtras of Patañjali, 3.1.[1]
Dhyāna
तत्र प्रत्ययैकतानता ध्यानम् ॥२॥
tatra pratyayaika-tānatā dhyānam ॥ 2 ॥
Dhyāna (meditation) is the one-pointedness of the mind on one image.
— Yoga Sūtras of Patañjali, 3.2.[1]
Samādhi
तदेवार्थमात्रनिर्भासं स्वरूपशून्यमिव समाधिः ॥३॥
tad evārtha-mātra-nirbhāsaṁ svarūpa-śūnyam iva samādhiḥ ॥ 3 ॥
Samādhi (absorption) is when that same dhyāna shines forth as the object alone and the mind is devoid of its own reflective nature.
— Yoga Sūtras of Patañjali, 3.3.[1]
त्रयमेकत्र संयमः ॥४॥
trayam ekatra saṁyamaḥ ॥ 4 ॥
When these three (dhāraṇā, dhyāna, samādhi) are performed together, it is called saṁyama.
— Yoga Sūtras of Patañjali, 3.4.[1]
English translations
I warmly recommend the translation and commentary by Edwin Bryant, The Yoga sūtras of Patañjali : a new edition, translation, and commentary with insights from the traditional commentators,[1] as it is highly readable but provides an in-depth introduction. For each sūtra it lists the Devanāgarī, the IAST roman transcription, a definition list of the individual words and a translation of the sūtra by the author. But best of all, then a brief discussion follows on the classical commentaries on that sūtra, with the summarizing thoughts and clarifications of Bryant. This was a great, thought-provoking and insightful way to study the sūtras. A highly recommended read that is sure to change your life in a positive way.