The festival of Maha Shivratri is looked upon with greatest reverence & respect by the devotees of Lord Shiva.
Date
This festival is celebrated every year on the 14th day in the Krishna Paksha of the month of Phalguna. As per the English calendar this is somewhere around February or March.
Legends
There are so many mythological stories associated with Shivaratri and they all hold this day as very auspicious day. During the samudramathana by the gods and demons, haalaa-hala a poison came out of the ocean. So toxic was it, that it would have wiped out the entire creation from this universe. At this juncture, as per the advice of Vishnu, gods approached Mahadev and prayed him to protect the life by consuming this poison. Pleased with their prayers, out of compassion for living beings, Shiva drank this poison and held it in his throat. The throat became blue due to this poison and Shiva was not harmed by this. Hence the names Neelakantha and Mrityunjaya. But the doctors advised gods to keep Shiva awake during the night as part of the therapy. To amuse Shiva, so that he doesn't fall asleep, gods took turn performing various dances and playing music. Thus the vigil was kept by the gods in contemplation of Shiva. As the day broke out, Shiva, pleased with their devotion blessed them all. Since then, on this day and night - devotees fast, keep vigil, sing glories of Lord and mediate.