Linum usitatissimum is an important cultivated, commercial and medicinal plant in the family Linacaea. This plant is also known as flax and their seeds are famous for their nutritional, medicinal and industrial purposes. Exploitation of Linum usitatissimum is context dependent. Commercially, it is used for manufacturing of linen fiber hence the name flaxseed is given to such a variety of Linum usitatissimum, on the other hand seeds of a variety used for many nutritional and industrial applications are called linseed. Linum usitatissimum is generally cultivated in areas having moderate to cold climate. The plant has a slender stem, lanceolate leaves and pale blue flowers with five petals. Canada, Russia, United States, China and India are among the top growers of Linum usitatissimum. Worldwide production of flax is 2.5-3 million tonnes per year. This plant is rich in pharmaceutical compounds along with some important nutraceuticals. Novel compounds found in flax are polyphenols, comprising of two major classes—lignans and neolignans. Lignans like secoisolariciresinol diglucoside (SDG) and lariciresinol diglucoside (LDG) are potential anticancer compounds whereas, neolignans such as dehydrodiconiferyl alcohol glucoside (DCG) and guaiacylglycerol-β-coniferyl alcohol ether glucoside (GGCG) are used in antimicrobial and anti-inflammatory drugs. However, the yield of these medicinal compounds in natural habitat is low and their extraction from wild is an expensive process. For this reason, researchers are busy devising cost effective, reproducible and practical strategies to enhance producton of lignans and neolignans in in vitro established infrastructure. In the first experiment, we established callus cultures of Linum usitatissimum following protocol of Anjum et al. (2016). These cultures were derived from stem explants obtained from in vitro seed derived aseptic plantlets. The objective of this study was to evaluate the effects of qualitative and quantitative differences in culture medium along with varying photoperiod treatments, on growth kinetics and secondary metabolites production in callus cultures of Linum usitatissimum. To this end, ~1 g callus was inoculated on three different culture media, namely Murashige and Skoog, Gamborg B5 and Schenk and Hildebrandt, and each culture on specific growth medium was kept under the influence of different photoperiod treatments viz. 16/8 h light and dark, continuous light and continuous dark, respectively. We observed differential effects of nutrient and photoperiods variation on growth kinetics and secondary metabolites xiii accumulation in callus cultures of Linum usitatissimum. Significant growth rate was observed on Gamborg B5 medium as compared to Murashige and Skoog medium, while Schenk and Hildebrandt medium showed a slow but steady growth response. Similarly, we observed that Gamborg B5 medium enhanced callus biomass (fresh weight 413 g/l anddry weight 20.7 g/l), phenolics production (667.60 mg/l), and lignan content (secoisolariciresinol diglucoside6.33 andlariciresinol diglucoside 5.22 mg/gdry weight respectively) at 16/8 h light and dark-week 4, while that of neolignans (dehydrodiconiferyl alcohol glucoside 44.42 and guaiacylglycerol-β-coniferyl alcohol ether glucoside 9.26 mg/g dry weight, respectively) at continuous dark-week 4. Conversely, maximum flavonoid production occurred at both Murashige and Skoog, Schenk and Hildebrandt media in the presence of continuous light. Generally, continuous dark had no significant role in any growth associated parameter. In the second experiment, we established cell suspension cultures of Linum usitatissimum by modifying method of Anjum et al. Simply, ~3g callus was inoculated into 100 ml liquid Murashige and Skoog medium and kept on a shaking incubator for 15 days in controlled conditions. Ten milliliters media containing viable cells was used as inoculum for establishment of cell suspension cultures. This experiment was aimed to enhance growth associated parameters and secondary metabolites accumulation with the help of repeated introduction of chemogenic silver nanoparticles at different stages, into cell suspension cultures of Linum usitatissimum. Repeated addition of silver nanoparticles enhanced biomass and polyphenols accumulation in cell suspension cultures. Adding silver nanoparticles on day 10 resulted in comparatively, highest production of lignans (secoisolariciresinol diglucoside, 252.75 mg/l; lariciresinol diglucoside, 70.70 mg/l), neolignans (dehydrodiconiferyl alcohol glucoside, 248.20 mg/l; guaiacylglycerol-β-coniferyl alcohol ether glucoside, 34.76 mg/l), total phenolic content (23.45 mg GAE/g DW), total flavonoid content (11.85 mg QUE/g DW) and biomass (dry weight: 14.5 g/l), respectively. Optimum production of both lignans and neolignans occurred on day 20 of culture; a 10-fold increase in secoisolariciresinol diglucoside, 2.8 fold increase in lariciresinol diglucoside, 5 fold increase in dehydrodiconiferyl alcohol glucoside and 1.75-fold increase in guaiacylglycerol-β-coniferyl alcohol ether glucoside was observed in production levels compared to control treatments, respectively. xiv In the third experiment, cell suspension cultures of Linum usitatissimum were exposed to repeated addition of biogenic zinc oxide nanoparticles in order to evaluate its effect on biomass accumulation and secondary metabolites production. Zinc oxide nanoparticles were added at three different stages and their results were compared to control treatments. Repeated elicitation of cell suspension cultures on day 0 and 15 resulted in highest fresh weight (412.16 g/l) and lignans production (secoisolariciresinol diglucoside 284.12 mg/l: lariciresinol diglucoside 86.97 mg/l). Contrarily, repeated elicitation on day 0 and 25 resulted in highest dry biomass (13.53 g/l), total phenolic production (537.44 mg/l), total flavonoid production (123.83 mg/l) and neolignans production (dehydrodiconiferyl alcohol glucoside 493.28 mg/l: guaiacylglycerol-β-coniferyl alcohol ether glucoside 307.69 mg/l). Enhancement of plant growth, free radical scavenging capacity and secondary metabolites accumulation was several fold greater than control treatments.