The inability to shrink silicon based electronic devices has lead to increasing interest in the field of nano-electronics. The use of individual molecule as component in electronic circuits has been at the forefront of most nano-electronic research in recent years. The technology based on use of molecules as circuit elements could play a prominent role in extending the current silicon based devices beyond the projected limits of CMOS scaling. It has been shown that conjugated molecules with appropriate pendant groups and end groups are capable of showing interesting electronic properties like conductance switching and NDR (Negative Differential Resistance). Even though there has been substantial amount of work done in this area there still remains several knowledge gaps which needs to be addressed. This book discusses the electronic properties of conjugated molecules along with conductance switching and self-assembly of alkanethiols to make molecular electronic circuits.