The Gemara in various places discusses the prohibitions involved in actual gambling, placing bets on various races, etc.  The concern is whether the winner is receiving money from someone who really does not want to give up his wager, and therefore the winner is taking money that has a tinge of “Gezaila”, thievery.  Also there is an opinion that even if this act of wagering is not in the category, the person involved in doing that, is wasting his time in action that is not beneficial to society.  The rules and guidelines for this are found in Masechat Sanhedrin, 27b, Shulchan Aruch, Choshen Mishpat 34, 16, and 370.

However, is participation in any lottery or raffle included in this category?  HaRav Ovadiah Hadoya, O.B.M. rules that such involvement in purchase of lottery tickets, etc., does not fit into the classification of the above type of gambling which is fraught with issurim, but rather this represents the function of a “goral” of joining with others in raising sums for various purposes.  The participants willingly make their purchases without any stigma of any illegal loss.  He cites the famous decisor R. Chaim Yosef Dovid Azulai, O.B.M., who describes the lotteries in Italy in raising sums for the acquisition of a Sefer Torah, etc.  (Birchei Yosef Yoreh Deah Kuntros Achron, 74).  

Consequently HaRav Ovadiah rules that purchase of lottery tickets is permissible.  (Of course it is understood that this hold true only if the individual does not become an addictive participant, etc.  (Yaskil Avdi VIII, Yoreh Deah, 5,3.)