By Swami Harshananda
Sometimes transliterated as: Maitrayaniya Upanisad, MaitrayaNiya Upanisad, Maitrayaniya Upanisad
Maitrāyanīya Upaniṣad is one of the more ancient Upaniṣads assigned to the period 2000 B. C. It is not classed among the major ones, since it was originally taught by the sage Maitri and belongs to the Maitrāyanīyaśākhā (śākhā = recension) of the Kṛṣṇa Yajurveda. The longer version as available now has seven prapāṭhakas or chapters and 73 mantras, both in prose and in poetry.
Content of Maitrāyanīya Upaniṣad
The Upaniṣad starts with the story of the king Bṛhadratha who renounced his kingdom and did severe austerities to realize the ātman. A sage named Śākāyanya came to his place whereupon the king fell at his feet and begged him to teach the Ātman. Being pleased with his earnest entreaties, the sage started teaching him.
The Vālakhilyas, the tiny sages, had got this wisdom from Kratu Prajāpati and the sage Maitri taught the same to Śākāyanya. The various and varied teachings of this Upaniṣad may be summarized as follows:
- The ātman, though encased in the body, is really free. This ātman is full of many blessed qualities and enlivens the body with consciousness
- The whole creation has emerged out of Prajāpati 
- In this body there are two selves, the jīva (individual Self) and the para (Supreme Self)
- The Para or Brahman is attained by vidyā (knowledge), tapas (austerity) and cintā (meditation)
- There are several gods like Agni (fire), Vāyu (air), Āditya (sun), and the trimurtis (Brahmā, Viṣṇu and Rudra) but they are all manifestations of the same Brahman
- Praṇava or Oṅkāra
- Three worlds bhuh, bhuvah and suvah
- Gist of the Gāyatrī mantra
- Taking food compared to a sacrifice
- Importance of time as a cosmic element
- Some methods of yoga which are similar to the ones described in the Yogasutras of Patañjali (200 B. C.)
- Description of the muktapuruṣa or the liberated person
- Mention of the kings of the Solar and the Lunar dynasties
- Knowledge of astronomy
- Familiarity with the Sāṅkhyan metaphysics
- Indication about the existence of the fine-arts like drawing and dramaturgy
- It is also known as the Maitri Upaniṣad.
- Prajāpati is the Lord of creatures.
- The Concise Encyclopedia of Hinduism, Swami Harshananda, Ram Krishna Math, Bangalore