The objective of this thesis is to develop a new type of fibres for concrete disperse reinforcement, investigate single fibre pull-out behaviour and fibre failure mechanisms, as well as study composite fibre performance in concrete tested in flexure. Presented fibres have high strength, low weight and are protected from corrosion. Fibres can be easily mixed into concretes with the different consistency. The thesis consists of an introduction, five main chapters, and conclusions. Chapter 2 describes the development of composite fibres and characterizes main properties of geometry and surface. The chapter covers the development of 3 fibre families (carbon, glass and hybrid), totally 14 different fibres with distinct diameter, shape and surface finish. Chapter 3 describes the development of 3 fine-grained concretes with compressive strength in the range of 40–120 MPa and main properties are characterized: fresh concrete consistency, hardened concrete strength and shrinkage. Chapter 4 describes single fibre pull-out experiments for three concrete matrices: high, medium and low strength concrete. Fibres placed in concrete with different configurations: 5–25 mm deep, as well as 0–60-degree angle. Chapter 5 describes fibre pull-out mechanisms and fibre failure mode analysis based on previous chapter experimental results. Chapter 6 presents composite fibre use in concrete as disperse reinforcement and beam behaviour in flexure is studied. Results and conclusions presented in this thesis show composite fibre positive potential to compete with widely used steel and polymer fibres as well as being superior in mechanics, technology and price.