Apparently ETA (Basque separatist organization) is responsible. http://edition.cnn.com/2006/WORLD/europe/12/30/madrid.blast/ Spanish PM suspends Eta dialogue http://news.bbc.co.uk/2/hi/europe/6219431.stm Eta warns peace process in crisis http://news.bbc.co.uk/2/hi/europe/5262938.stm Bombing people is couterproductive. I initially thought the Madrid blast might have been in sympathy to Saddam Hussein. Meanwhile in Thailand - Bangkok explosions leave two dead http://news.bbc.co.uk/2/hi/asia-pacific/6221177.stm Thai believe that opponents of the current military government are involved, and not necessarily outside militant groups. I seems that access to explosives is rather easy, or perhaps those with access to explosives are more likely to use them these days.