The assembly line is one of the major systems in any manufacturing industry, where several finished components are brought together and assembled sequentially leading to the customer ready product. This chapter discusses several contributions associated with the complexities and corresponding methods and approaches in finding optimal solutions. The reconfigurable manufacturing systems are very much required to accommodate the flexibility in assembly line. It is very much demanded and indirectly driven by the market trend. The methods such as Linear Programming minimizing the overall cost of the workstation activation and reconfiguration, cycle time are discussed along with the maximization of the process quality of the assembly tasks. Moreover, automated storage/retrieval system optimization using numerical simulations are described. The work associated with the energy consumption minimization with a view point of assembly line balancing and control systems using genetic algorithm as well as particle swarm optimization, artificial immune systems have been discussed. The chapter also discusses the disassembly process efficiency maximization using genetic algorithms, goal programming and artificial bee colony algorithm using several case studies. The chapter elaborates certain test cases of two-sided assembly line balancing using several exact methods. Lastly, the Industry-4.0 approaches such as considering late customization, Resequencing Assembly lines have also been reviewed.