Denna licentiatavhandling handlar om lediga hyreslägenheter. I avhandlingens första del beskrivs och analyseras dels hur problemet med lediga lägenheter ser ut på den svenska bostadshyresmarknaden under åren 1990-1994 och dels hur problemet hanteras av svenska kommunala bostadsföretag. Dataunderlaget har insamlats via enkäter och hämtats från offentlig statistik. I avhandlingens andra del görs en litteraturundersökning som leder vidare till en bestämning av begrepp, relevanta att använda vid teoretiska analyser av vakansgrader på en marknad. Resultaten i den första delen visar att de lediga lägenheterna på bostadshyresmarknaden koncentrerats till vissa delmarknader. Lägenheterna karakätiseras av egenskaper som gör dem oattraktiva på marknaden, alternativt för dyra. Företagen hanterar problemet lediga lägenheter på sätt som kan försklaras av marknadsmodellen monopol, nämligen genom prisanpassningari form av prisdiskriminaering och kvantitetsanpassningar i form av rivning. Rivning har använts i oväntat stor omfattning, ca 3% av företagens bestånd har rivits under den undersökta perioden. Sänkt hyra har inget smaband med efterfrågeförändringar, däremot med utbudsförändringar i form av ökad konkurrens. Flera resultat av den statistiska analysen pekar spledes mot att marknadsstrukturen har betydelse för att förutsäga hur de kommunala bostadsföretagen kommer att agera i situationer som kräver pris- eller kvantitetsanpassningar. Företagen har också använt sig av olika slag av kortsiktiga kvantitetsanpassningar, vilket är intressant ur teoretisk synpunkt därför att man inte bruka r tala om kvantitetsanpassningar på kort sikt. Genomgången av vetenskaplig litterautr i anhandlingens andra del, visar att begreppet naturlig vakansgrad är ett etablerat teoretiskt begrepp men att det hittills varken är entydgit definierat eller entydigt använt. För att råda bot på detta göra en bestämning och komplettering av de begrepp som används för att analysera vakanser med metodiken kvalitativ komparativ statik. Begreppen är gilitga både för marknadsmodellen perfekt konkurrens och marknadsmodellen monopolitsisk konkurrens och enheterna kan vara antal lägenheter såväl som antal veckor. / This licentiate thesis treats the problem of vacancies in the rental housing market. THe first part of the thesis consists of an empirical study aimed at enlighten how the vacancies are handled by Swedish Municipal Housing Companies between the years 1990 and 1994. THe data is collected through a postal survey which was sent to a choice of Swedish Municipal Housing Companies, namely those companies with a high overall vacancy rate so that it could be expected that these companies have a vacancy problem. The results of the survey is structured in a way that make them possible to relate to economic theory and conduct an analysis in terms of what kinds of adjustments have been made by the companies as a response to exogenic changes on the local housing market. IN a descriptive part of the results, it becomes clear that housing vacancies are concentrated to certain submarkets, which means that on these submarkets the vacancy rate can be very high. The submarkets are characteristically neighbourhoods built either during the sities, the so called million homes programme, which often means a less attractive location or appearence, or neighbourhoods built later which often means high rents. The companies handle the vacancies in a way that can be explained by the market models monopolistic competition as well as monopoly. Price adjustments are conducted as different forms of price discrimination, for instance lower rents for young people. THe companies have demolished apartments, which is a quantity adjustment. Demolitions have been used to a surprisingly great extent. Three percent of the total stock of these companies has been demolished during a period of five years. THe statistical analysis shows that a lowered rent has no connection with changes in demand bur it has connection with changes in supply in fomrs of an increased number of apartments in nearby substitute markets, for instance an increase of condominiums and rental apartments owned by other municipal housing companies. Several results of the statistical analyses implies that the market structure is of importance when predicting how a municipal housing company will act in situations demanding price- or quantity adjustments. A theoretically interesting result is that the companies have invented different forms of short-run quantity adjustments, for instance locking one bedroom in a two-bedroom apartment and lease it as a one-bedroom apartment. Among theorists there are different opinions on whether the short run supply curve for housing is fixed or not. The findings here could be an argument against a fixed short run supply curve. The second part of the thesis consists of a literature study. In analysing wellknown papers on vacancies it is found that although "the natural vacancy rate" is an established concept there is need for a definition. Therefore the concept is analysed and defined. Five related vacancy concepts are suggested: 1) observed vacancy rate, 2) natural vacancy rate in short run equilibrium, 3) deviation of vacancy rate in short run equilibrium, 4) natural vacancy rate in long run equilibrium and 5) deviation of natural vacancy rate in long run equilibrium. These concepts are useful in analysing vacancies whether the units are number of apartments or number of weeks. To measure vacancies in time is of great importance to be able to analyse vacancy persistence. / <p>QC 20151216</p>