Method for installing and/or maintaining an elevator installation comprising a counterweight and a guide rail system , the guide rail system comprising: at least one guide rail for guiding a counterweight and/or an elevator car of the elevator installation ; and at least one counterweight holder ; characterized in that the guide rail has at least one opening ; and in that the counterweight holder comprises: a support for supporting the counterweight ; and a hook element for fastening the support to a guide rail of the elevator installation , it being possible to form-fittingly fasten the support to the guide rail by hooking the hook element into an opening in the guide rail , the hook element being hooked into the opening in the guide rail such that the support is form-fittingly fastened to the guide rail ; the at least one counterweight holder holding the counterweight , the method comprising: hooking the at least one counterweight holder into the at least one opening in the at least one guide rail such that the support of the at least one counterweight holder is form-fittingly fastened to the at least one guide rail ; and arranging the counterweight on the at least one counterweight holder such that the counterweight is held by the at least one counterweight holder . at least one guide rail for guiding a counterweight and/or an elevator car of the elevator installation ; and at least one counterweight holder ; characterized in that the guide rail has at least one opening ; and in that the counterweight holder comprises: a support for supporting the counterweight ; and a hook element for fastening the support to a guide rail of the elevator installation , it being possible to form-fittingly fasten the support to the guide rail by hooking the hook element into an opening in the guide rail , the hook element being hooked into the opening in the guide rail such that the support is form-fittingly fastened to the guide rail ; the at least one counterweight holder holding the counterweight , the method comprising: hooking the at least one counterweight holder into the at least one opening in the at least one guide rail such that the support of the at least one counterweight holder is form-fittingly fastened to the at least one guide rail ; and arranging the counterweight on the at least one counterweight holder such that the counterweight is held by the at least one counterweight holder . a support for supporting the counterweight ; and a hook element for fastening the support to a guide rail of the elevator installation , it being possible to form-fittingly fasten the support to the guide rail by hooking the hook element into an opening in the guide rail , the hook element being hooked into the opening in the guide rail such that the support is form-fittingly fastened to the guide rail ; the at least one counterweight holder holding the counterweight , the method comprising: hooking the at least one counterweight holder into the at least one opening in the at least one guide rail such that the support of the at least one counterweight holder is form-fittingly fastened to the at least one guide rail ; and arranging the counterweight on the at least one counterweight holder such that the counterweight is held by the at least one counterweight holder . hooking the at least one counterweight holder into the at least one opening in the at least one guide rail such that the support of the at least one counterweight holder is form-fittingly fastened to the at least one guide rail ; and arranging the counterweight on the at least one counterweight holder such that the counterweight is held by the at least one counterweight holder . <EOS>