Ericulture plays vital role in rural livelihood security especially among relegated and weaker sections of the society. All operations from rearing to weaving are done mostly by women folk. As a result, it has received the most interest from rural residents in India’s North Eastern area, where it is also practiced by women as a hobby. The polyphagous Eri silkworm (Samia ricini) has been studied by numerous researchers, and their feeding habits on a variety of plant species have led to the classification of host plants as primary viz., Castor (Ricinus communis) and Kesseru (Heteropanax fragrans), secondary like Tapioca (Manihot esculanta), Borpat (Ailanthus grandis), Borkesseru (Ailanthus excelsa) and Payam (Evodia flaxinifolia), and tertiary, viz., Ailanthus glandulosa, Ailanthus tryphysa, Carica papaya, Gmelina arborea. Among these plants, castor (Ricinus communis L.) is a significant main food plant. Eri silkworms should be raised on castor to maximize potential output and produce basic seed. However, because castor is an annual plant and requires yearly recurring costs to establish systematic plantations, it has restricted its proliferation in the field. India and the rest of the world have invested a great deal of effort in genetically enhancing castor to increase its output of seeds and oil. Not much research, meanwhile, has been done to genetically improve castor in terms of biomass and plant habit in order to use it for ericulture where leaf yield is more important than seed and oil yield. Success of any host plant improvement program depends on the variability of traits in the germplasm bank. A well-characterized and conserved gene pool is essential for the breeders to select desirable parents for initiating a directional breeding program and to remove duplicates in the gene bank, so castor germplasm has been collected, characterized, and documented in descriptor cum catalogues at CMER&TI, Jorhat, Assam, which is helpful in castor breeding for selection and development of genotypes with higher vegetative biomass and perennial in nature to reduce recurrent cultivation costs. Castor-related information like taxonomy, genetics, cytogenetics, physiology and phenology, pest and diseases, and bioassays with reference to ericulture in Northeastern India has been discussed in this chapter where bioassay studies have also been included. Opportunities and challenges related with castor cultivation for ericulture have also been discussed.