Vasudeva Dwadashi or Vasu Dev Dwadasi is the Dwadasi day dedicated to Lord Vasudeva (Lord Sri Krishna). Vasudev Dwadasi falls on Ashada Shudda Dwadasi, just a day after Shayana Ekadasi or Deva Sayani Ekadashi. In 2009, the date of Vasudeva Dwadashi Vratam is July 4, Saturday. According to Puranas, Lord Vishnu represents Ekadasi and Goddess Mahalakshmi represents Dwadasi.
On Vasudeva Dwadasi, devotees of Sri Krishna recite Krishna stotras and worship Lord Sri Krishna. Some devotees donate cow to please Lord Krishna. Godaanam (Donating cow) is the most meritorious deed performed on Vasu Deva Dwadasi. Performing puja to cow is the most recommended ritual to do on Vasudev Dwadashi. Vasudeva Dwadasi is also observed as Vamana Dwadashi.
Shiva Shayana Vrata – Siva Sayana Vratam or Shiva Dolotsavam
Chaturmasya Vrata – Chatur Mas Vrat
Chaturmas Vrata Niyama – Rules and Codes of Chatur Mas Vratam
Chatur Mas Vrata Phalam – Merits of Chaturmasa Vratam
Time to observe Chatur Mas Vrata - When is Chaturmas Vrata observed?
[...] Chaturmas Vrata is the observance that is performed for four holy months as per Hinduism. Chatur Mas Vratam begins either in Ashada masam on Ekadasi or Dwadashi or on Pournami day when Sun enters into Karka (Cancer) rashi. According to major Panchangas, in 2009, the date of Chaturmasa Vratam Arambh is on july 4, Saturday. Ashada Shudda Dwadashi is also observed as Vasudeva Dwadashi. [...]