Navaratri (Sanskrit: नवरात्रि, romanized: Navarātri) is an annual Hindu festival observed in honor of the goddess Durga, an aspect of Adi Parashakti, the supreme goddess. It spans over nine nights, first in the month of Chaitra (March/April of the Gregorian calendar), and again in the month of Ashvin (September–October). It is observed for different reasons and celebrated differently in various parts of the Hindu - Indian cultural sphere. Theoretically, there are four seasonal Navaratris. However, in practice, it is the post-monsoon autumn festival called Sharada Navaratri. There are also 2 Gupta Navaratris or "Secret Navaratris" as well, one starting on the Shukla Paksha Pratipada of the Magha Month (Magha Gupta Navaratri) and another starting in the Shukla Paksha Pratipada of Ashadha Month.

The word Navarātram means "a period of nine nights" in Sanskrit, nava meaning "nine" and ratri meaning "night".

In the eastern and northeastern states of India, the Durga Puja is synonymous with Navaratri, wherein goddess Durga battles and emerges victorious over the buffalo demon Mahishasura to help restore dharma. In southern states, the victory of Durga or Kali is celebrated. In the western state of Gujarat, Navaratri celebrations are constituted by arti, followed by garba. In all cases, the common theme is the battle and victory of good over evil based on a regionally famous epic or legend such as the Devi Mahatmya.

Celebrations include worshipping nine goddesses during nine days, stage decorations, recital of the legend, enacting of the story, and chanting of the scriptures of Hinduism. The nine days are also a major crop season cultural event, such as competitive design and staging of pandals, a family visit to these pandals, and the public celebration of classical and folk dances of Hindu culture. Hindu devotees often celebrate Navaratri by fasting. On the final day, called Vijayadashami, the statues are either immersed in a water body such as a river or an ocean, or the statue symbolising the evil is burnt with fireworks, marking the destruction of evil. During this time preparations also take place for Deepavali (the festival of lights) which is celebrated twenty days after Vijayadashami.

According to some Hindu texts such as the Shakta and Vaishnava Puranas, Navaratri theoretically falls two or four times in a year. Of these, the Sharada Navaratri near the September equinox (the autumn equinox in September–October) is the most celebrated and the Vasanta Navaratri near the March equinox (the spring equinox in March–April) is the next most significant to the culture of the Indian subcontinent. In all cases, Navaratri falls in the bright half (waxing phase) of the Hindu lunisolar months. The celebrations vary by region, leaving much to the creativity and preferences of the Hindu.

Sharada Navaratri is the most celebrated of the four Navaratri, named after Sharada which means autumn. It commences on the first day (pratipada) of the bright fortnight of the lunar month of Ashvin. The festival is celebrated for nine nights once every year during this month, which typically falls in the Gregorian months of September and October. The exact dates of the festival are determined according to the Hindu lunisolar calendar, and sometimes the festival may be held for a day more or a day less depending on the adjustments for sun and moon movements and the leap year. In many regions, the festival falls after the autumn harvest, and in others, during harvest.

The festivities extend beyond goddess Durga and various other goddesses such as Saraswati and Lakshmi. Deities such as Ganesha, Kartikeya, Shiva, and Parvati are regionally revered. For example, a notable pan-Hindu tradition during Navaratri is the adoration of Saraswati, the Hindu goddess of knowledge, learning, music, and arts, through Ayudha Puja. On this day, which typically falls on the ninth day of Navaratri, peace and knowledge is celebrated. Warriors thank, decorate, and worship their weapons, offering prayers to Saraswati. Musicians upkeep, play, and pray their musical instruments. Farmers, carpenters, smiths, pottery makers, shopkeepers, and all sorts of tradespeople similarly decorate and worship their equipment, machinery, and tools of trade. Students visit their teachers, express respect, and seek their blessings. This tradition is particularly strong in South India, but is observed elsewhere too.

Chaitra Navaratri, also called Vasantha Navaratri, is the second most celebrated Navaratri, named after vasanta which means spring. It is observed during the lunar month of Chaitra (March–April). The festival is devoted to goddess Durga, whose nine forms are worshipped on nine days. The last day is also Rama Navami, the birthday of Rama. For this reason, it is also called Rama Navaratri by some people.