**1. Introduction**

Rapid development and increase growth of population has led to global environmental problems. Furthermore, increasing demand on energy source has contributed to a reduction of

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petroleum reverse. To overcome this problem, production of biofuel from renewable resour‐ ces such as biomass and biofiber has gain great attention to partially replace fossil fuels in the future.Productionofbiofuelfromthesematerials isenvironmentfriendlyandsustainable.Mass production of biomass and biofiber as waste residue from agriculture and forestry industry has createdagreat concernfor environment sustainabilityglobally.Generally,biomassandbiofiber can be generated from various origin either direct cultivation, or as residue from agro-waste and forestry industries. The biomass and biofiber residue generated from these industries including sugarcane, bagasse, rice straw, empty fruit bunch (EFB), oil palm trunk (OPT), oil palm frond (OPF), and sago bark. Meanwhile,the examples forthe cultivated biofiber are kenaf and hemp.

In order to produce biofuel from these materials, it has to undergo few processes such as biomass production, pretreatment, saccharification, and fermentation. Pretreatment of biomass has been reported to contribute substantial portion of liquid biofuel production cost. There are four established pretreatment methods such as thermal, chemical, biological, and physical pretreatment that have been applied to pretreat biomass and biofiber. However, among of the pretreatments mentioned, physical pretreatment method especially irradiation method is considered as one of the promising approaches applied to reduce the recalcitrant of biomass and biomaterials. Generally, this method utilizes both thermal and non-thermal effect generated by intermolecular collision during the realignment of biomass molecule. Irradiation pretreatment offers great advantages such as having very selective process, and it is energy efficient. Since there are wide ranges of tropical biomass types renewably available in tropical country, thus, exploring the potential of this pretreatment is really much needed.

This chapter discusses comprehensively on irradiation pretreatment of tropical biomass prior to the subsequent enzymatic saccharification and fermentation processes. The emphasis is given on the type of irradiation pretreatments and mechanism that could be beneficial for scientists and researchers to understand the process, which can be applied as an alternative pretreatment approach for biofuel production.
