An installation package for a wind turbine, the installation package comprising: an assembly for use in installation of a wind turbine tower; and a tower section of the wind turbine tower comprising a plurality of engagement guides on or adjacent to an upper inner edge of the tower section to guide the assembly while it is lowered into the tower section; the assembly comprising: an installation unit for installation within the tower section of the wind turbine tower, the installation unit comprising a plurality of circumferentially spaced-apart unit guides, each of the unit guides being configured to engage a corresponding engagement guide on or adjacent to an upper inner edge of the tower section to guide the assembly while it is lowered into the tower section; and a yoke releasably connected to the installation unit and comprising a plurality of circumferentially spaced-apart yoke guides, each of the yoke guides being configured to engage a corresponding engagement guide on or adjacent to the upper inner edge of the tower section to guide the assembly while it is lowered into the tower section; the assembly being configured such that, while the assembly is being lowered, at least one of the unit guides and/or the yoke guides is or are substantially continuously engaged with the engagement guides from when the assembly enters the tower section until the assembly reaches its installation position within the tower section. an assembly for use in installation of a wind turbine tower; and a tower section of the wind turbine tower comprising a plurality of engagement guides on or adjacent to an upper inner edge of the tower section to guide the assembly while it is lowered into the tower section; the assembly comprising: an installation unit for installation within the tower section of the wind turbine tower, the installation unit comprising a plurality of circumferentially spaced-apart unit guides, each of the unit guides being configured to engage a corresponding engagement guide on or adjacent to an upper inner edge of the tower section to guide the assembly while it is lowered into the tower section; and a yoke releasably connected to the installation unit and comprising a plurality of circumferentially spaced-apart yoke guides, each of the yoke guides being configured to engage a corresponding engagement guide on or adjacent to the upper inner edge of the tower section to guide the assembly while it is lowered into the tower section; the assembly being configured such that, while the assembly is being lowered, at least one of the unit guides and/or the yoke guides is or are substantially continuously engaged with the engagement guides from when the assembly enters the tower section until the assembly reaches its installation position within the tower section. an installation unit for installation within the tower section of the wind turbine tower, the installation unit comprising a plurality of circumferentially spaced-apart unit guides, each of the unit guides being configured to engage a corresponding engagement guide on or adjacent to an upper inner edge of the tower section to guide the assembly while it is lowered into the tower section; and a yoke releasably connected to the installation unit and comprising a plurality of circumferentially spaced-apart yoke guides, each of the yoke guides being configured to engage a corresponding engagement guide on or adjacent to the upper inner edge of the tower section to guide the assembly while it is lowered into the tower section; the assembly being configured such that, while the assembly is being lowered, at least one of the unit guides and/or the yoke guides is or are substantially continuously engaged with the engagement guides from when the assembly enters the tower section until the assembly reaches its installation position within the tower section.