Temperature and sunlight intensity are the main ecological conditions that influence the biochemical pathways of the grapes, with sunlight exposure been associated with an improvement in grape quality, resulting in grapes that are richer in soluble solids, phenolic and volatile organic compounds, especially anthocyanins and terpens, and lower titratable acidity. The intensity and quality of sunlight exposure, especially UV radiation and the complex interaction with temperature affect the biosynthesis of various phenolic and volatile compounds- proantocyanidins, antocyanins, favonols, terpens- by altering their gene expression. Leaf removal in the cluster zone is one of the commonly applied viticultural practices used to increase light penetration and to decrease humidity in dense foliage. The timing of leaf removal plays a major role in the synthesis of different polyphenolic and volatile compounds in grapes, since they are synthesized at different times during berry ripening. The influence of timing of leaf removal on the content and composition of volatile compounds in red grape varieties is poorly investigated. Today's viticulture and wine production is facing new challenges in terms of climate change. Climatic changes can affect the relationship between the variety and its environmental conditions, thereby changing the time of occurrence of certain phenophases and the quantity and quality of the grapes. Considering the above, it is necessary to investigate earlier timings of leaf removal and its effect on the grape volatile and phenolic content, in order to better adapt to recent climate changes. Due to above, two- year study (2018/2019) has been carried out on the 'Merlot' variety grown in the vineyard in the continental part of Croatia, Zagreb vineyard hills, to study the effects of basal leaf removal on canopy microclimate and to evaluate the justification of the different timings of leaf removal in relation to the volatile and phenolic profile of grape variety 'Merlot' (Vitis vinifera L.). Meteorological data of mezoclimatic measurements of the vineyard and microclimatic measurements of the vine (canopy temperature, UV radiation and relative humidity) were recorded simultaneously at the meteorological station installed inside the vineyard. The first chapter, Introduction, focuses on the problem of research on climate influence on the chemical composition of grapes, which is sometimes difficult to interpret, because climate implies a large number of environmental conditions (temperature, humidity, rainfall, sunlight), each of which plays an important role in the growth and development of vines and grapes. Furthermore, the amount of phenolic and volatile compounds and their precursors varies within and between climate zones. Topographic characteristics of the vineyard, such as elevation, slope, and exposure of the terrain, as well as the orientation of vine rows in the vineyard, vigor of the vineyard, and different viticultural practices, can result in great variability in microclimatic conditions, especially the quality and intensity of sunlight. The hypotheses that were established and tested in this study are: (1) early leaf removal will reduce the yield and the content of total acids and increase of sugar content in the grapes of the 'Merlot' variety, (2) early leaf removal will increase the content of polyphenolic and volatile compounds in 'Merlot' grapes in compare to control treatment. The second chapter, Overview of the Previous Research, starts with the overview of the berry development and the timing of synthesis of different secondary metabolites. Phenolic and volatile composition (anthocyanins, flavonols, flavan-3-ols, stilbenes, terpenes, volatile acids, alcohols and carbonyls) of the grape skins and their contibution to the grape quality are also reviewed. The main part od the chapter focuses on related research on the microclimate of the vines and their influence on the grape quality. Previous research showed that microclimatic conditions within the grapevine canopy- temperature and solar radiation, are important parameters that directly regulate grape ripening parameters: sugars, organic acids and secondary metabolites. UVB radiation is important for the chemical composition and quality of grapes, since some phenolic and volatile compounds have the function of absorbing and screening UVB radiation and protecting the plant from its harmful effects. Solar radiation has been reported to increase sugar content and pH in grape juice and increase phenolic and volatile content in grapes. It is therefore important to evaluate different canopy manipulation treatments and their effects on grape microclimatic conditions, as they may contribute to the accumulation of numerous chemical components, especially the phenolic and volatile content of grapes. Leaf removal in the cluster zone is a common canopy management practice used to manipulate microclimate of grapevines by increasing light penetration and temperature in the fruiting zone and reducing canopy density, which affects relative humidity and reduces the incidence of pests and diseases. By improving microclimatic conditions and balancing the ratio of older, less photosynthetically active leaves to younger, more photosynthetically active leaves, basal leaf removal can improve grape and wine composition by increasing the content of polyphenolic and volatile compounds and reducing titratable acidity. The third chapter, Materials and methods, provides all the information on how the research was conducted. The research was conducted in 2018. and 2019. on the Jazbina experimental field of the Department of Viticulture and Enology, Faculty of Agriculture, University of Zagreb, on the grape variety 'Merlot', planted in 2005. The vineyard is located on the slope with slightly southwestern exposure. The vines were subjected to cultural practices common to continental Croatia. Data for daily air temperatures and precipitation for both seasons were obtained from a weather station located in the vineyard. The experiment was conducted with five treatments; no leaf and lateral shoot removal, basal leaf removal and lateral shoot removal performed before flowering, at berry set, at grape closure and at the beginning of veraison, with 4 basal leaves and all lateral shoots per shoot removed. Leaf removal treatments were repeated on the same vines during the two years. Relative humidity, temperature and UVA+UVB radiation inside the foliage at the cluster level of the control treatment and when leaf removal was performed at berry set were continuously monitored (frequency of 1 second) throughout the growing season. During vegetation, for each vine in the experiment, the number of buds per vine, the number of shoots per vine and the number of fruit bearing shoots per vine were counted, from which the number of clusters per bud, the number of clusters per shoot and the number of clusters per cluster carrying shoot were calculated. The leaf area was calculated on vine basis. Grape harvest was determined by weekly monitoring the content of soluble solids, titratable acidity and pH. Merlot was harvested manually in the morning hours. Yield was measured on the vine basis, together with counting the number of clusters per vine. The grapes from each block of each treatment were manually pressed to obtain the must, from which soluble solids, titratable acidity and pH was measured. Content of phenolic and volatile compounds in grape berry skin was analysed according to the methods of Tomaz and Maslov (2016) and Šikuten et al. (2021), respectively. All data were analyzed using analysis of variance (treatment, year). In the chapters Results and Discussion, all the research results are presented and discussed: weather conditions and phenological phases, canopy microclimatic conditions, vine growth and yield components, soluble solids, titratable acidity and pH at harvest, as well as total phenolic and volatile content of berry skin at harvest. Leaf removal altered microclimate by increasing the UV radiation within the grape zone. By improving the mycoclimate of the vines, leaf removal increased in the content of polyphenolic compounds - anthocyanins, flavanols, flavan-3-ols and hydroxycinnamic acids. Leaf removal reduced the content of C6 volatile compounds, that give green and vegetal aromas. The ratio of leaf area to yield and bud fruitfulness was not affected by leaf removal. Eary leaf removal (before flowering and at the time of berry setting) increased the content of polyphenolic compounds and decreased the content of volatile C6 compounds in grape skins. Eary leaf removal (before flowering) incresead the sugar content and reduced the yield of the 'Merlot' variety, but only in one year of research. Leaf removal performed after flowering reduced total acidity in the must. Removal of basal leaves at the time of berry setting and grape closure did not affect the sugar content in the must, while leaf removal carried out at the beginning of the veraison led to an increase in the sugar content in the must compared to the control. Modification of the canopy microclimate can signifficantelly improve phenolic and volatile composition of the grapes, and therefore contribute to the grape quality. These results revealed important difference in leaf removal efficiency on phenolic content of the grapes in different ecological conditions during ripening, with leaf removal having a higher influence on the grape phenolic content in a season with the cooler grape ripening conditions. Early leaf removal can lead to a positive effect on the quality of 'Merlot' grapes under the environmental conditions in which the present study was undertaken but particular attention has to be given to the ecological conditions of the vegetative season.