There are a number of species assessment systems in place to check out the threat status of a species. Of these, the system proposed by IUCN is the most widely accepted. A leading organisation in management of natural resources, IUCN is also a pioneer in developing an assessment system of global Red List of threatened species and has been continuing to do so over the last 47 years. Now, The IUCN Red List of Threatened Species is a brand. The global IUCN Red List is updated on a regular basis. The latest version was released in October 2010 as ‘2010.4’ (IUCN Red List, 2010c). Initially, experts alone used to compile a Red List; but since 1994 appropriate conservation and environmental organizations and expert networks are involved in the assessment process through a rigorous process of data collection on certain criteria, validation of collected data, scoring, and assigning of Red List categories (IUCN Red List, 2010c). There are 9 or 11 categories (varies between global and regional/national assessments), but only three of these qualify as threatened categories: Critically Endangered (CR), Endangered (EN) and Vulnerable (VU). Each of these categories has its own set of criteria defining the category (IUCN, 2003; IUCN Red List, 2010a). In addition to global species assessments, national red listing is also necessary to take conservation measures of threatened species in the national context. Therefore, the global assessment criteria need to be modified to reflect country’s situation (IUCN Bangladesh, 2000; IUCN, 2003). In Bangladesh, IUCN Bangladesh set a good example of such adaptation in the late 1990’s by preparing the Red Books of threatened animals of Bangladesh in five volumes covering the Red List, fish, amphibians & reptiles, birds, and mammals. Later on, IUCN Bangladesh translated these books into Bangla in a single volume (IUCN Bangladesh, 2003). Regarding the threatened flora, as mentioned at the beginning of this paper, Khan et al. (2001) still remains the only Red Data Book on vascular plants of Bangladesh. Some important issues associated with this book are discussed in the following sections. The issues concerning threatened plant species of Bangladesh were first presented in the early nineties (Khan, 1991; Khan et al., 2001). The published list of 12 vascular plants was based on the field experience of experts rather than following any standard quantitative or semi-quantitative methods. According to the ‘IUCN Red List of Threatened Plants’ of 1997, 24 plant species of Bangladesh faced various degrees of threat of extinction (IUCN, 1997, in Nishat et al., 2002). Despite the importance of identifying threatened species in plant conservation, no concrete measures were taken by any government or non-government agencies until 1998 when a project was launched by the Bangladesh National Herbarium supported by Bangladesh Agriculture Research Council (Khan et al., 2001). IUCN Red List categories and criteria of 1994 were apparently followed to determine threatened vascular plant species. Out of 106 species listed in this book, 1 is Critically Endangered (CR), 1 Endangered (EN), 2 Vulnerable (VU), 3 Lower Risk (LR), 25 Data Deficient (DD), and 74 are Not Evaluated (NE). Almost at the same time, under the National Conservation Strategy (NCS) Implementation Project-1, an attempt was made to determine the threatened categories of plant species found in 10 different ecologically important areas/ecosystems, but it was insufficiently planned and incomplete (MoEF, 2001). Later on, Khan (2003) mentioned 95 vascular plants as threatened (92 angiosperms and three gymnosperms) without citing any references. Threatened status of plant and animal species from Bangladesh is regularly recorded in the Global IUCN Red List. For example, in the Global Red List 2006, 12 plant species were recorded as threatened; in 2010 it is 16 (IUCN Red List, 2010d). By consulting eight volumes of ‘Encyclopedia of Flora and Fauna of Bangladesh’ (Volumes 5-12) on vascular plants (pteridophytes, gymnosperms and angiosperms) (Siddiqui et al., 2007a, b; Ahmed et al., 2008b, c; Ahmed et al., 2009a, b, c, d), about 13% species were found designated as threatened (Table 1). A few families are significantly threatened: for example, about 53% species of Orchidaceae are threatened (94 species out of 179), whereas in Lamiaceae it is more than 30% (26 species out of 86). Needless to say, these threatened statuses are purely in the national context. The information presented in the Encyclopedia can be considered as the most recent update for Bangladesh.