According to scholars, the symbolic concept of Ardhanārīśvara lies in germinal form, in the Yama-Yamī Saṃāda of Veda. In Vṛhadāraṇyaka Upaniṣad Parama Puruṣa was not capable of any kind of pleasure, being all alone, so he divided his soul into male and female, here also lies the seed of the Ardhanārīśvara concept. Again, in Śverāśvetara Upamniṣad, Brahman has been called ātmayoni, and this has been viewed as the bisexual manifestation of Rudra-Śiva. In the later part of this śloka he is again called kṣetrajñapatiḥ, so the sāṃkhya-philosophical concept of prakṛti and puruṣa has been conjoined in the term ̍patiḥ̍. Scholars think that the philosophical base of Śiva̍s ardhanārīśvara self, as Mircea Eliade has put so nicely–
“Divine bisexuality is one of the many formulae of the totality-unity signified by the union of couples of opposites: masculine-feminine, visible-invisible, heaven-earth, light-darkness, as also goodness-wickedness, creation-destruction etc.

In Mahābhārata, when Upamanyu was praising Mahādeva, he indicated to the form of ardhanārīśvara, among his many other forms, saying– “his consort Pārvatī is held on the other half of his body–
kasya cārdhe sthitā kantā anaṅgaḥ kena nirjitaḥ.
Upamanyu says, “I bow to that form of Śiva, who is wearing a coronate, half of a necklace and half keyūra, and kuṇḍala in his ear.

Here the commentator has commented, since the other half of Śiva is ̍feminine̍, the references to the ornaments have come.

dehārdhasya strīrūpatvāt.

The Liṅgapurāṇa says, at the end of one kalpa, Brahmā sat for tapasyā, but could not create anything new. Out of anger and frustration on himself, tears came out of his eyes. And from that tear, emerged ghosts. Seeing the abundance of ghosts in the very beginning of creation, Brahmā was very upset, and he thought of immolating himself. But at that very moment, Rudra came out of Brahmā̍s mouth. And the shape of that Rudra-Śiva was Ardhanārīśvara. Dividing that form, Rudra-Śiva created Umā-Maheśvarī out of himself.

In philosophical conception, śakti and śaktimān are one, and that is why comes the conceptualisation of Ardhanārīśvara. Śiva and Śivānī are two forms of one entity– to establish this, comes the concept of Ardhanārīśvara.

According to Purāṇa, once Pārvatī, seeing the reflection of herself in the heart of Śiva, thought that some other lady remains in the heart of her husband. She was irritated, and Śiva told her the truth, convinced her in several ways. Afterwards, when she realised her mistake, she felt ashamed of her suspicion. Now she said to Śiva, “Just as my shadow resides in your heart, I wish that my corporeal frame also reside in your body. You embrace me physically all the time– let it be so.”

Śiva said, “So be it. You take half of my body, or let me take half of your body. Let half of my body be feminine, and the other masculine. If uyou can divide yourself in two, I̍ll take half of your body and incorporate it into mine.” Goddess Pārvatī said, “I wish two make two bodies one. If you take half of my body, I would also like to to take half of yuor body. Śiva accepted her proposal. They will remain in an unified entity, together and inseparable. God Śiva took half of the goddess̍s female body and beca,e Ardhanārīśvara. This incident is described similarly, though somewhat brief, in Nārada-Pañcarātra.

In Vāyupurāṇa and Brahmāṇḍapurāṇa it is said that– from the wrath of Brahmā, emerged a Deity with the combined body of male and female; and he is Ardhanārīśvara Śiva. Later, this body got divided into two separate entities– Śiva and Durgā. Here, the original form itself was that of Ardhanārīśvara.

In the Pratimā-lakṣaṇ adhyāya of Matsyapurāṇa, there is description of Ardhanārīśvara. On the side of Gpd Śiva, there will be part of the young moon(vālachandrakalā), attached to his matted locks and on the other half, on the side of Umā, there will be the sign of tilaka and parted hair. Vāsuki, king of the snakes, will be around the right ear of this combined form, and on the left ear, there will be kuṇḍala. On the right side, there will be atrident or human skull in the hand of Śiva, and on the left side, a lotus or a mirror will be held in the hand of Pārvatī. The left arm of the left sidewill be decorated with armlets and bangles, and the scred thread will be in its proper place. On the left side, the breast and the lower portion will be heavy and well-built. On the right side– which belongs to Śiva, the liṅga (linga,phallus) covered with tiger-skin, will be upheld. There will be girdle around the waist in the left part, and the right side will be surrounded by a snake. The right foot of God Mahādeva will be on a lotus, and on the left side, Parvatī̍s foot, decorated with anklet and jewels, will be placed a little higher. There will be rings on all the fingers.The foot of Pārvatī will be dyed with red colour. This is the form of Ardhanārīśvara — god Śiva on the one side and Pārvatī on the other–
ardhena devadevasya nārīrūpaṃ suśobhanaṃ
ardhanārīśvarasyedaṃ rūpamasminnudāhṛtam.

In Śāradātilaka-tantra, there is a description of Ardhanārīśvara–
nīlapravālaruciraṃ vilasattrinetraṃ
pāśāruṇotpala-kapāla-triśūla-hastam
ardhāmvikeśamaniśaṃ pravibhakta-bhūṣaṃ
vālenduvaddha-mukuṭaṃ praṇamāmi rūpam.

However, a brilliant description of Ardhanārīśvara is given by Vidyāpati of Mithilā.
jaya jaya śankara jaya trpurāri
jaya adha-puruṣa jayati adha-nārī.
ādha dhavala tanu ādhā gorā
ādha sahaja kuca ādha kaṭorā.
ādha hāḍamāla ādha gajamoti
ādha cānana śobhe ādha vibhūti.
ādha cetana mati ādha bhorā
ādha paṭora ādha munja dorā.
ādha yoga ādha bhoga vilāsā
ādha pidhāna ādha naga vāsā.
ādha canda ādha sindura śobhā
ādha virūpa ādha jga lobhā.
bhane kaviranjana vidhātā jāne
dui kae bnāṭala eka parāṇe.