Women have been involved in computers since computers were first envisioned. They are present in all facets of computing and information technology. Despite this, their presence is comparatively small in these fields; see statistics below.
When America's first electronic computer, ENIAC, was developed, its programmers were women. Jennifer S. Light's essay, "When Computers Were Women," documents and describes the role of the women of ENIAC and outlines the historical omission or downplay of women's roles in computer science history..
A proposal from an economical standpoint suggests that in order to avert the computing and IT industry from dangers such as global sourcing, a solution is needed to increase the participation of underrepresented groups like women. 
It has also been claimed that there is a growing demand for IT workers with leadership, interpersonal, and communication skills in order to combat the general drop in worker retention and ineffective training. In particular, the cost of replacing a skilled technical employee has been estimated to be as high as 120% of the yearly salary of the position. Furthermore, over 50% of 900 IT leaders in the US who were surveyed cited retention of skilled professionals as a primary concern.  In addition, leaders with business and soft skills are sought after. Qualitative studies shows that many women in technology are interested in this combination of technical and non-technical work, hence they are potentially a good fit in these roles.
On a similar note, it has been argued that the inclusion of women in computing will mitigate innovation-hindering effects such as groupthink by preventing the group from becoming too homogenized. Gender diversity has been suggested to give benefits such as better decision making, increased creativity, and enhanced, innovative performances. 
The book Gender and Computers : Understanding the Digital Divide claims that the lack of participation of females in computing excludes them from the "new economy", which calls for sophisticated computer skills in exchange for high salary positions.  A consequence from such exclusion will likely result in further social and gender inequality.
For the most recent statistics on women's participation in information and computing education and workforce, see the National Center for Women & IT (NCWIT) By the Numbers or the Microsoft-funded NCWIT Scorecard: A Report on the Status of Women in Information Technology.
Although 37.1% of US Computer Science degrees were awarded to women in 1984, the number has been decreasing over time: from 1989-1990, 29.9% of Computer Science degrees were awarded to women and from 1997-1998, only 26.7% of the same degree's recipients were women. Similar figures are given by alternative sources: Women’s share of bachelor degrees in the computer and information sciences increased steadily through the mid-1980s where women earned 37% of the 38,878 degrees conferred in 1984–85. The number of the same degrees awarded to women has been increasing since 1992–93, yet the percentage awarded to women was down to 22% in 2005.
It is worth noting, however, that the pattern for Master’s degrees is somewhat different : the number and percentage of degrees earned by women is slowly, but steadily increasing to a high of 5,432 or 34% in 2000–01 (NCES, 2002).
Although teenage girls are now using computers and the Internet at rates similar to their male peers, they are five times less likely to consider a technology-related career or plan on taking post-secondary technology classes. The National Center for Women & Information Technology reports that of the SAT takers who intend to major in computer and information sciences, the proportion of girls has steadily decreased relative to the proportion of boys, from 20 percent in 2001 to 12 percent in 2006. The total number of these students (boys and girls) has also been decreasing since 2001, when it peaked at 73,466.
According to a College Board report, among SAT takers in 2006, slightly more girls than boys reported to having "course work or experience" in computer literacy, word processing, internet activity, and creating spreadsheets/databases. More boys than girls (59% vs 41%) reported course work or experience with computer programming. Of the 146, 437 students (13%) who reported having no course work or experience, 61% were girls and 39% were boys.
Many more boys than girls take Advanced Placement (AP) Computer Science exams. According to the College Board  in 2006, 2,594 girls and 12,068 boys took the AP Computer Science A exam, and 517 girls and 4,422 boys took the more advanced AP Computer Science AB exam. From 1996 to 2004, girls made up 16–17% of those taking the AP Computer Science A exam and around 10% of those taking AP Computer Science AB exam.
Women’s representation in computer and information sciences workforce hovers about 30%. From 1993 through 1999, NSF’s SESTAT reported the percentage of women working as computer / information scientists (including those who hold a bachelor’s degree or higher in an S&E field or have a bachelor’s degree or higher and are working in an S&E field) declined slightly from 33.1% to 29.6% percent while the absolute numbers increased from 170,500 to 185,000 (NSF, n.d.).
A study of over 7000 high school students in Vancouver, Canada showed that the degree of interest in the field of Computer Science for teenage girls is comparably lower than that of teenage boys.  The same effect is seen in higher education; for instance, only 4% of female college freshmen expressed intention to major in Computer Science in the US. 
However, in both the U.S. and Canada, several structural and policy features of educational systems reduce the likelihood that either boys or girls will even know computer science exists as a discipline of study or that it is somehow different from computer literacy skills they have learned. The focus of computing education in North America over the past three decades has been on information fluency and literacy (i.e., computer use), rather than on teaching the concepts of computing or computational thinking. As a result, where computer science is taught, it is usually as an elective class, and in many school districts, even labeled as "vocational" -- courses university-bound students and their parents avoid. In addition, elective courses are scheduled against other electives in which many students and their parents have emotional or financial investments (e.g., orchestra); they are typically scheduled during the same period as courses that strengthen students’ college applications, such as foreign language courses. Low course demand is reinforced by the lack of computer science coursework in college admissions requirements. Not surprisingly, most college-bound high school students, male and female alike, have little understanding of what computer science majors study and often equate computing to programming. In the U.S., a federal educational policy makes it difficult for teachers to integrate computational thinking into the mainstream curriculum see Cohoon and Aspray, Women and Information Technology Research on Underrepresentation for the most up to date and comprehensive reviews of literature on women in K12 and undergraduate computing. In part to qualify for federal education funding distributed through the states, most U.S. states and districts now focus on ensuring that all students are at least “proficient” in mathematics and reading, making it difficult for teachers to focus on teaching concepts beyond the test. According to a Rand Corporation study , such a concentration on testing can cause administrators to focus resources on tested subjects at the expense of other subjects (e.g., science) or distract their attention from other needs. Thus, despite the availability of the Computer Science Teachers Association ACM Model Curriculum for K-12 Computer Science, computational thinking is unlikely to be taught either standalone or as integrated into other areas of study (e.g., mathematics, biology) anytime in the near future. The National Center for Women & IT distributes free resources for increasing awareness of the need for teaching computer science in schools, including the "Talking Points" card Moving Beyond Computer Literacy: Why Schools Should Teach Computer Science.
According to a 1998-2000 ethnographic study by Jane Margolis and Allan Fisher at Carnegie Mellon University, men and women viewed computers very differently. Women interviewees were more likely to state that they saw the computer as a tool for use within a societal and/or interdisciplinary context than did the men interviewed. On the other hand, men were more likely to express an interest in the computer as a machine. Moreover, women interviewed in the Margolis et al. study perceived that many of their male peers were "geeks," with limited social skills. Females often disliked the idea that computers "become their life."  The students observed and interviewed in that study were probably not representative of students in general, since at that time, in order to be admitted to CMU Computer Science a student needed to have some programming experience. More research is needed to understand the generalizability of Margolis' and Fisher's findings.
From a two year research initiative published in 2000 by AAUW, young girls in focus groups reported that "lack of interest" was not the reason for steering away from a computing career, but rather, their male peers were treating computers as toys. They expressed distaste in boys' behavior. Still, the National Assessment of Educational Progress showed as far back as 2000 that boys and girls use computers at about the same rates, albeit for somewhat different purposes.
Nearly 1000 students in University of Akron were surveyed, and it was discovered that females hold a more negative attitude towards computer than males.  Another study assessed the computer-related attitude of over 300 students in University of Winnipeg and obtained similar results. 
This is thought to contribute to the gender disparity phenomenon in computing, in particular the females' early lack of interest in the field. 
See Chapter 5, Cohoon and Aspray A Critical Review of the Research on Women’s Participation in Postsecondary Computing Education for a comprehensive review of literature on barriers to women in undergraduate computing. Factors shown in research include:
Like the pre-college situation, solutions are most often implemented outside of the mainstream (e.g., providing role models, mentoring, and women’s groups), which can also create the perception among women, their male peers, and their professors that to be successful, women need “extra help” to graduate. Most people do not realize that the “extra help” is not academic, but instead access to the kind of peer networks more readily available to male students. Many women decline to participate in these extracurricular support groups because they do not want to appear deficient. In short, the conditions under which women (and underrepresented minority students) study computing are not the same as those experienced by men.