This book presents important research from around the world in the field of Antisense molecules which interact with complementary strands of nucleic acids, modifying expression of genes. Some regions within a double strand of DNA code for genes, which are usually instructions specifying the order of amino acids in a protein along with regulatory sequences, splicing sites, non-coding introns and other complicating details. For a cell to use this information, one strand of the DNA serves as a template for the synthesis of a complementary strand of RNA. The template DNA strand is called the transcribed strand with antisense sequence and the mRNA transcript is said to be sense sequence (the complement of antisense). Because the DNA is double-stranded, the strand complementary to the antisense sequence is called non-transcribed strand and has the same sense sequence as the mRNA transcript (though T bases in DNA are substituted with U bases in RNA). Many forms of antisense have been developed and can be broadly categorised into enzyme-dependent antisense or steric blocking antisense.